#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;
using ll = long long;

const ll modc = 998244353;
class mint {
    ll x;
public:
    mint(ll x=0) : x((x%modc+modc)%modc) {}
    mint operator-() const {
      return mint(-x);
    }
    mint& operator+=(const mint& a) {
        if ((x += a.x) >= modc) x -= modc;
        return *this;
    }
    mint& operator-=(const mint& a) {
        if ((x += modc-a.x) >= modc) x -= modc;
        return *this;
    }
    mint& operator*=(const  mint& a) {
        (x *= a.x) %= modc;
        return *this;
    }
    mint operator+(const mint& a) const {
        mint res(*this);
        return res+=a;
    }
    mint operator-(const mint& a) const {
        mint res(*this);
        return res-=a;
    }
    mint operator*(const mint& a) const {
        mint res(*this);
        return res*=a;
    }
    mint pow(ll t) const {
        if (!t) return 1;
        mint a = pow(t>>1);
        a *= a;
        if (t&1) a *= *this;
        return a;
    }
    mint inv() const {
        return pow(modc-2);
    }
    mint& operator/=(const mint& a) {
        return (*this) *= a.inv();
    }
    mint operator/(const mint& a) const {
        mint res(*this);
        return res/=a;
    }
    bool operator == (const mint& a) const{
        return x == a.x;
    }
    friend ostream& operator<<(ostream& os, const mint& m){
        os << m.x;
        return os;
    }
    friend istream& operator>>(istream& ip, mint&m) {
        ip >> m.x;
        return ip;
    }
};

int main(){

    int N;
    char c;
    string S;
    cin >> N >> S;
    vector<vector<vector<mint>>> dp(N+1, vector(2, vector<mint>(2)));
    dp[0][0][0] = 1;
    for (int i=1; i<=N; i++){
        c = S[i-1];
        if (c != 'a') dp[i][0][0] += dp[i-1][0][0];
        if (c != 'a') dp[i][0][1] += dp[i-1][0][0] * (c-'b');
        dp[i][0][1] += dp[i-1][0][1] * 25;
        if (c != 'a') dp[i][1][0] += dp[i-1][1][0];
        else dp[i][1][0] += dp[i-1][0][0];
        if (c != 'a') dp[i][1][1] += dp[i-1][0][0];
        if (c != 'a') dp[i][1][1] += dp[i-1][1][0] * (c-'b');
        dp[i][1][1] += dp[i-1][0][1];
        dp[i][1][1] += dp[i-1][1][1] * 25;
    }

    cout << dp[N][1][1] << endl;
}