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

#define ll long long

ll M = 998244353;

void solve(string &s) {
    int n = s.size();
    vector<ll> dp1 (n, 0);
    vector<ll> pop1(6, 0);
    dp1[0] = 1;
    for (int i = 1; i < n; i++) {
        dp1[i] = (2*dp1[i-1]-(pop1[s[i]-'a'])+M*M)%M;
        pop1[s[i]-'a'] = dp1[i-1];
    }
    vector<ll> dp2 (n, 0);
    vector<ll> pop2(6, 0);
    dp2[0] = 1;
    for (int i = 1; i < n; i++) {
        dp2[i] = (2*dp2[i-1]-2*(pop2[s[i]-'a'])+M*M)%M;
        pop2[s[i]-'a'] = dp2[i-1];
    }
    cout << (dp1[n-1]-dp2[n-1]+M)%M << '\n';
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n, q;
    cin >> n >> q;
    string s;
    cin >> s;
    s = '_'+s;
    solve(s);
    for (int i = 0; i < q; i++) {
        int x;
        char c;
        cin >> x >> c;
        s[x] =c;
        solve(s);
    }
}