#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
using i64 = int64_t;
using u64 = uint64_t;
#define rep(i,n) for(int i=0; i<(n); i++)


const i64 MOD = 998244353;

int main() {
  int N; cin >> N;
  string S; cin >> S;
  i64 ans = 1;
  rep(i,N-1) if(S[i] != '?' && S[i] == S[i+1]) ans = 0;
  rep(i,N-2) if(S[i] != '?' && S[i] == S[i+2]) ans = 0;
  vector<int> C(N);
  rep(i,N) if(S[i] == '?'){
    int t = 26;
    if(i >= 1) t--;
    if(i >= 2) t--;
    if(i < N-1) if(S[i+1] != '?') t--;
    if(i < N-2) if(S[i+2] != '?') t--;
    ans = ans * t % MOD;
  }
  cout << ans << endl;
  return 0;
}


struct ios_do_not_sync{
  ios_do_not_sync(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
  }
} ios_do_not_sync_instance;