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#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,b) for (int i = (a); i <= (b); ++i)
#define REPD(i,a,b) for (int i = (a); i >= (b); --i)
#define FORI(i,n) REP(i,1,n)
#define FOR(i,n) REP(i,0,int(n)-1)
#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define vi vector<int>
#define ll long long
#define SZ(x) int((x).size())
#define DBG(v) cerr << #v << " = " << (v) << endl;
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++)
#define fi first
#define se second

const int N = 50500;
const int M = 222;
const int DD = 6;
const int mod = 998244353;

template<int A>
class value {
public:
	int coeff[A];
	value() {
		FOR(i,A) coeff[i] = 0;
	}
	int calc(vi vals) {
		int ans = 0;
		FOR(i,A) ans = int((1LL*coeff[i]*vals[i] + ans) % mod);
		return (ans+mod)%mod;
	}
	value operator* (int x) const {
		if (x < 0) x = (x%mod + mod) % mod;
		value ans = *this;
		FOR(i,A) ans.coeff[i] = int((1LL*ans.coeff[i]*x) % mod);
		return ans;
	}
	value operator+ (const value &v) const {
		value ans = *this;
		FOR(i,A) ans.coeff[i] = (ans.coeff[i] + v.coeff[i]) % mod;
		return ans;
	}
	void clear() {
		FOR(i,A) coeff[i] = 0;
	}
};

int n,q;
int ans;
char s[N];
int c_prev[M][DD], last_pos[M][DD];

int m;
int n_lo[M], n_hi[M];
int get_seg_id[N];

vector<int> wvals[M], uvals[M];

int cpos[DD];

int D = 6;

/// ------------------------------ D = 6 -------------------------------

value<DD+1> w[N], wprv, wcur[DD];
value<DD*DD> u[N], ucur[DD*DD];

void calc_seg(int seg_id) {
	int lo = n_lo[seg_id], hi = n_hi[seg_id];
	
	FOR(i,D) {
		cpos[i] = -1;
		wcur[i].clear();
		wcur[i].coeff[i] = 1;
		last_pos[seg_id][i] = -1;
	}
	wprv.clear();
	wprv.coeff[D] = 1;
	FOR(i,D*D) {
		ucur[i].clear();
		ucur[i].coeff[i] = 1;
	}
	
	for (int k = lo; k < hi; k++) {
		
		int ch = s[k]-'a';
		
		w[k] = wprv*2 + wcur[ch]*(-1);
		wcur[ch] = wprv;
		wprv = w[k];
		
		u[k].clear();
		FOR(i,D) u[k] = u[k] + ucur[ch*D+i];
		FOR(i,D) {
			ucur[ch*D+i].clear();
			ucur[i*D+ch] = u[k];
		}
		
		cpos[ch] = k;
		
		last_pos[seg_id][ch] = k;
	}
}


int getw(int k) {
	int seg_id = get_seg_id[k];
	return w[k].calc(wvals[seg_id]);
}

int getu(int k) {
	int seg_id = get_seg_id[k];
	return u[k].calc(uvals[seg_id]);
}


void calc_glob(int seg_id = 0) {
	
	FOR(i,D) c_prev[0][i] = -1;
	//FOR(j,m) {
	for (int j = seg_id; j < m; j++) {
		FOR(i,D) c_prev[j+1][i] = last_pos[j][i] == -1 ? c_prev[j][i] : last_pos[j][i];
	}
	
	if (wvals[0].empty()) {
		FOR(j,m) {
			wvals[j].resize(D+1);
			uvals[j].resize(D*D,0);
		}
	}
	//FOR(j,m) FOR(i,D*D) uvals[j][i] = 0;
	for (int j = seg_id; j < m; j++) FOR(i,D*D) uvals[j][i] = 0;
	
	FOR(i,D) wvals[0][i] = -1;
	wvals[0][D] = 0;
	FOR(i,D) uvals[0][i*D+i] = 1;
	
	//FOR(j,m) {
	for (int j = seg_id; j < m; j++) {
		int lo = n_lo[j];
		FOR(i,D) {
			int pos = c_prev[j][i];
			if (pos == -1) wvals[j][i] = -1;
			else wvals[j][i] = getw(pos-1);
		}
		wvals[j][D] = j == 0 ? 0 : w[lo-1].calc(wvals[j-1]);
		/*printf("%d : ", j);
		FOR(i,D*D) printf("%d ", uvals[j][i]);
		printf("\n");*/
		vector<int> ui(6);
		FOR(i,D) {
			int pos = c_prev[j][i];
			if (pos != -1) ui[i] = getu(pos);
		}
		FOR(i,D) {
			int pos = c_prev[j][i];
			if (pos == -1) uvals[j][D*i+i] = 1;
			else uvals[j][D*i+i] = ui[i];
			FOR(i2,D) {
				int pos2 = c_prev[j][i2];
				if (pos2 > pos) uvals[j][D*i+i2] = (uvals[j][D*i+i2] + ui[i2]) % mod;
			}
		}
		/*printf("%d : ", j);
		FOR(i,D*D) printf("%d ", uvals[j][i]);
		printf("\n");
		FOR(i,D) printf("%d ", c_prev[j][i]);
		printf("\n");*/
	}
	/*printf("u = ");
	FORI(i,n) printf("%d ", getu(i));
	printf("\n");*/
	
	int wans = getw(n);
	int uans = 0;
	FOR(i,D) {
		int pos = c_prev[m][i];
		if (pos != -1) uans = (uans + getu(pos)) % mod;
	}
	ans = (wans + mod - uans) % mod;
	//printf("%d %d\n", wans, uans);
	//printf("\n");
}

/// ------------------------------ D = 2 -------------------------------

value<3> w2[N], wprv2, wcur2[2];
value<4> u2[N], ucur2[4];

void calc_seg2(int seg_id) {
	int lo = n_lo[seg_id], hi = n_hi[seg_id];
	
	FOR(i,D) {
		cpos[i] = -1;
		wcur2[i].clear();
		wcur2[i].coeff[i] = 1;
		last_pos[seg_id][i] = -1;
	}
	wprv2.clear();
	wprv2.coeff[D] = 1;
	FOR(i,D*D) {
		ucur2[i].clear();
		ucur2[i].coeff[i] = 1;
	}
	
	for (int k = lo; k < hi; k++) {
		
		int ch = s[k]-'a';
		
		w2[k] = wprv2*2 + wcur2[ch]*(-1);
		wcur2[ch] = wprv2;
		wprv2 = w2[k];
		
		u2[k].clear();
		FOR(i,D) u2[k] = u2[k] + ucur2[ch*D+i];
		FOR(i,D) {
			ucur2[ch*D+i].clear();
			ucur2[i*D+ch] = u2[k];
		}
		
		cpos[ch] = k;
		
		last_pos[seg_id][ch] = k;
	}
}


int getw2(int k) {
	int seg_id = get_seg_id[k];
	return w2[k].calc(wvals[seg_id]);
}

int getu2(int k) {
	int seg_id = get_seg_id[k];
	return u2[k].calc(uvals[seg_id]);
}


void calc_glob2(int seg_id = 0) {
	
	FOR(i,D) c_prev[0][i] = -1;
	//FOR(j,m) {
	for (int j = seg_id; j < m; j++) {
		FOR(i,D) c_prev[j+1][i] = last_pos[j][i] == -1 ? c_prev[j][i] : last_pos[j][i];
	}
	
	if (wvals[0].empty()) {
		FOR(j,m) {
			wvals[j].resize(D+1);
			uvals[j].resize(D*D,0);
		}
	}
	//FOR(j,m) FOR(i,D*D) uvals[j][i] = 0;
	for (int j = seg_id; j < m; j++) FOR(i,D*D) uvals[j][i] = 0;
	
	FOR(i,D) wvals[0][i] = -1;
	wvals[0][D] = 0;
	FOR(i,D) uvals[0][i*D+i] = 1;
	
	//FOR(j,m) {
	for (int j = seg_id; j < m; j++) {
		int lo = n_lo[j];
		FOR(i,D) {
			int pos = c_prev[j][i];
			if (pos == -1) wvals[j][i] = -1;
			else wvals[j][i] = getw2(pos-1);
		}
		wvals[j][D] = j == 0 ? 0 : w2[lo-1].calc(wvals[j-1]);
		/*printf("%d : ", j);
		FOR(i,D*D) printf("%d ", uvals[j][i]);
		printf("\n");*/
		vector<int> ui(6);
		FOR(i,D) {
			int pos = c_prev[j][i];
			if (pos != -1) ui[i] = getu2(pos);
		}
		FOR(i,D) {
			int pos = c_prev[j][i];
			if (pos == -1) uvals[j][D*i+i] = 1;
			else uvals[j][D*i+i] = ui[i];
			FOR(i2,D) {
				int pos2 = c_prev[j][i2];
				if (pos2 > pos) uvals[j][D*i+i2] = (uvals[j][D*i+i2] + ui[i2]) % mod;
			}
		}
		/*printf("%d : ", j);
		FOR(i,D*D) printf("%d ", uvals[j][i]);
		printf("\n");
		FOR(i,D) printf("%d ", c_prev[j][i]);
		printf("\n");*/
	}
	/*printf("u = ");
	FORI(i,n) printf("%d ", getu(i));
	printf("\n");*/
	
	int wans = getw2(n);
	int uans = 0;
	FOR(i,D) {
		int pos = c_prev[m][i];
		if (pos != -1) uans = (uans + getu2(pos)) % mod;
	}
	ans = (wans + mod - uans) % mod;
	//printf("%d %d\n", wans, uans);
	//printf("\n");
}

int qpos[N];
char qc[N];

int main() {
	scanf("%d%d", &n, &q);
	//FORI(i,n) s[i] = 'a' + rand()%2;
	//FORI(i,q) {
	//	qpos[i] = rand()%n + 1;
	//	qc[i] = 'a' + rand()%2;
	//}
	scanf(" %s", s+1);
	FOR(i,q) scanf("%d %c", &qpos[i], &qc[i]);
	D = 0;
	FOR(i,n) D = max(D, s[i]-'a'+1);
	FOR(i,q) D = max(D, qc[i]-'a'+1);
	
	m = sqrt(n); // m = 100, L = 500?
	m = min(m, 120);
	//m = 2;
	FOR(j,m) {
		n_lo[j] = j*n/m + 1;
		n_hi[j] = (j+1)*n/m + 1;
		for (int i = n_lo[j]; i < n_hi[j]; i++) get_seg_id[i] = j;
	}
	
	if (D == 2) {
		FOR(j,m) calc_seg2(j);
		calc_glob2();
	} else {
		FOR(j,m) calc_seg(j);
		calc_glob();
	}
	printf("%d\n", ans);
	
	FOR(i,q) {
		int pos = qpos[i];
		char c = qc[i];
		s[pos] = c;
		
		int seg_id = get_seg_id[pos];
		if (D == 2) {
			calc_seg2(seg_id);
			calc_glob2(seg_id);
		} else {
			calc_seg(seg_id);
			calc_glob(seg_id);
		}
		printf("%d\n", ans);
	}
	return 0;
}