#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
#define rep(i,n) for(int i=0; i<(n); i++)


int main(){
    int N; cin >> N;
    string S; cin >> S;

    i64 dp[2][2] = {}; // [is same][used 'a']
    dp[1][0] = 1;

    for (char c : S) {
        i64 ci = c - 'a';
        i64 nxdp[2][2] = {};

        nxdp[0][0] += dp[0][0] * 25;
        nxdp[0][1] += dp[0][1] * 25;
        nxdp[0][1] += dp[0][0];

        if (ci == 0) {
            nxdp[1][1] += dp[1][0];
        }
        else {
            nxdp[1][0] += dp[1][0];
            nxdp[1][1] += dp[1][1];
            nxdp[0][0] += dp[1][0] * (ci - 1);
            nxdp[0][1] += dp[1][1] * (ci - 1);

            nxdp[0][1] += dp[1][0];
        }

        rep(s, 2) rep(t, 2) dp[s][t] = nxdp[s][t] % 998244353;
    }

    cout << dp[0][1] << endl;
    return 0;
}




struct ios_do_not_sync {
    ios_do_not_sync() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} ios_do_not_sync_instance;