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#include <bits/stdc++.h>
using namespace std;

constexpr int MAX_N = 5e4;
constexpr long long MOD = 998244353;

int n, q, p;
string s;
char z;

vector<int> last = vector<int>(6);
long long dp1[MAX_N + 1] = {1}, dp2[MAX_N + 1];

int solve() {
    fill(last.begin(), last.end(), 0);

    for(int i = 1; i <= n; i++) {
        dp1[i] = (dp1[i - 1] << 1);

        if(dp1[i] > MOD) {
            dp1[i] -= MOD;
        }

        if(last[s[i]] > 0) {
            dp1[i] -= dp1[last[s[i]] - 1];

            if(dp1[i] < 0) {
                dp1[i] += MOD;
            }
        }

        last[s[i]] = i;
    }

    fill(last.begin(), last.end(), 0);

    for(int i = 1; i <= n; i++) {
        dp2[i] = (int)(last[s[i]] == 0);

        for(int j = 0; j < 6; j++) {
            if(last[s[i]] <= last[j]) {
                dp2[i] += dp2[last[j]];

                if(dp2[i] > MOD) {
                    dp2[i] -= MOD;
                }
            }
        }

        last[s[i]] = i;
    }

    long long sum = 0;

    for(int i = 0; i < 6; i++) {
        sum += dp2[last[i]];
    }

    sum %= MOD;

    return (((dp1[n] - 1 - sum) % MOD) + MOD) % MOD;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);

    cin >> n >> q;
    cin >> s;

    s = '#' + s;
    for(int i = 1; i <= n; i++) {
        s[i] -= 'a';
    }

    cout << solve();

    for(int i = 1; i <= q; i++) {
        cin >> p >> z;
        s[p] = z - 'a';

        cout << '\n' << solve();
    }
}