#include <iostream>
using namespace std;
typedef long long ll;

const ll MOD = 998244353;

ll dp[4];

int main()
{
    int n;
    string s;
    cin >> n >> s;
    dp[0] = 1;
    for(int i = 0; i < n; i++){
        ll d[4];
        if(s[i] == 'a'){
            d[0] = 0;
            d[1] = dp[0];
            d[2] = dp[2] * 25 % MOD;
            d[3] = dp[3] * 25 % MOD;
        }
        else{
            d[0] = dp[0];
            d[1] = dp[1];
            d[2] = (dp[0] * (s[i] - 'b') + dp[2] * 25) % MOD;
            d[3] = (dp[0] + dp[1] * (s[i] - 'b') + dp[2] + dp[3] * 25) % MOD;
        }
        swap(dp, d);
    }
    cout << (dp[3]) % MOD << endl;
}