#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;

const ll MOD = 998244353;

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

  ll dp1[N][26];
  memset(dp1, 0, sizeof(dp1));
  ll dp2[N][26];
  memset(dp2, 0, sizeof(dp2));
  int a_cnt = 0;

  for (int i = 0; i < N; ++i) {
    int d = S[i] - 'a';

    if (i == 0) {
      for (int v = d - 1; v >= 0; --v) {
        if (v == 0) {
          dp2[i][v] += 1;
        } else {
          dp1[i][v] += 1;
        }
      }
    } else {
      for (int v = d - 1; v >= 0; --v) {
        if (v == 0 && a_cnt > 0) continue;
        if (a_cnt >= 2) continue;

        if (a_cnt == 0) {
          if (v == 0) {
            dp2[i][v] += 1;
            dp2[i][v] %= MOD;
          } else {
            dp1[i][v] += 1;
            dp1[i][v] %= MOD;
          }
        } else {
          dp2[i][v] += 1;
          dp2[i][v] %= MOD;
        }
      }

      for (int v = 25; v >= 0; --v) {
        for (int u = 25; u >= 0; --u) {
          if (v == 0) {
            dp2[i][v] += dp1[i - 1][u];
            dp2[i][v] %= MOD;
          } else {
            dp1[i][v] += dp1[i - 1][u];
            dp2[i][v] += dp2[i - 1][u];

            dp1[i][v] %= MOD;
            dp2[i][v] %= MOD;
          }
        }
      }
    }

    if (d == 0) {
      ++a_cnt;
    }

    /*
    for (int d = 0; d < 26; ++d) {
      cerr << dp1[i][d] << " ";
    }
    cerr << endl;
    for (int d = 0; d < 26; ++d) {
      cerr << dp2[i][d] << " ";
    }
    cerr << endl;
    */
  }

  ll ans = 0;

  for (int d = 0; d <= 25; ++d) {
    ans += dp2[N - 1][d];
    ans %= MOD;
  }

  cout << ans << endl;

  return 0;
}