#include <bits/stdc++.h>
#include <atcoder/math>
using namespace std;
using namespace atcoder;
#define int long long
using vec_int = vector<int>;
using vec_ii = vector<vec_int>;
using vec_iii = vector<vec_ii>;
using vec_iiii = vector<vec_iii>;
using P = pair<int,int>;
using T = tuple<int,int,int>;
using ll = long long;
using ld = long double;
#define rep(i, n) for(int i = 0; i < (int)(n); i++)

void cout_line(vector<int> &a){
    for(int i=0;i<a.size();i++){
        if(i<a.size()-1){
            cout<<a.at(i)<<" ";
        }else{
            cout<<a.at(i)<<endl;
        }
    }
}

int charToInt(char c){
    char zero_num = '0';
    return (int)c - (int)zero_num;
}

signed main(){
    int N; cin>>N;
    string S; cin>>S;
    int MOD = 998244353;

    rep(i, S.size()-1){
        if(S.at(i)!='?'&&S.at(i+1)!='?'){
            if(S.at(i)==S.at(i+1)){
                cout<<0<<endl;
                return 0;
            }
        }
    }
    rep(i, S.size()-2){
        if(S.at(i)!='?'&&S.at(i+2)!='?'){
            if(S.at(i)==S.at(i+2)){
                cout<<0<<endl;
                return 0;
            }
        }
    }
    int ans = 1;
    rep(i, S.size()){
        if(S.at(i)=='?'){
            int minus = 0;
            if(i>0)minus++;
            if(i>1)minus++;
            if(N-i>1){
                if(S.at(i+1)!='?'){
                    minus++;
                }
            }
            if(N-i>2){
                if(S.at(i+2)!='?'){
                    minus++;
                }
            }
            ans *= 26-minus;
            ans %= MOD;


        }
    }
    cout<<ans<<endl;



    return 0;
}