#include <bits/stdc++.h>   using namespace std;   const int mod = 998244353;   int main() {     ios::sync_with_stdio(false);     long long n;     cin >> n;     string s;     cin >> s;     if (s[0] == s[n - 1]) {       char a = s[0];       char b = s[n - 1];       long long x = 0, y = 0;       for (int i = 0; s[i] == a; i++) {         x++;       }       for (int i = n - 1; s[i] == b; i--) {         y++;       }       cout << ((x + 1) * (y + 1)) % mod;     } else {       char a = s[0];       char b = s[n - 1];       long long x = 0, y = 0;       for (int i = 0; s[i] == a; i++) {         x++;       }       for (int i = n - 1; s[i] == b; i--) {         y++;       }       cout << (x + y + 1) % mod;     }     return 0;   }   