#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic pop
using namespace std;
using namespace atcoder;
#define rep(i,n)for (int i = 0; i < int(n); ++i)
#define rrep(i,n)for (int i = int(n)-1; i >= 0; --i)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
template<class T> void chmax(T& a, const T& b) { a = max(a, b); }
template<class T> void chmin(T& a, const T& b) { a = min(a, b); }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;
using mint = modint998244353;

mint dp[2][2], ndp[2][2];

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  string s;
  cin >> s;
  dp[0][0] = 1;
  for(char c: s) {
    rep(i, 2) rep(j, 2) ndp[i][j] = 0;
    if (c == 'a') {
      ndp[0][1] += dp[0][0];
      ndp[1][0] += 25 * dp[1][0];
      ndp[1][1] += dp[1][0] + 25 * dp[1][1];
    } else {
      int k = c - 'a';
      ndp[1][1] += dp[0][0] + (k - 1) * dp[0][1] + dp[1][0] + 25 * dp[1][1];
      ndp[1][0] += (k - 1) * dp[0][0] + 25 * dp[1][0];
      ndp[0][0] += dp[0][0];
      ndp[0][1] += dp[0][1];
    }
    rep(i, 2) rep(j, 2) dp[i][j] = ndp[i][j];
  }
  mint ans = dp[1][1];
  cout << ans.val() << endl;
}