#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pint = pair<int, int>;
using pll = pair<ll, ll>;

int main(){
    const ll mod = 998244353;
    int N; cin >> N;
    string S; cin >> S;
    vector<ll> pat(N, 1);
    if(S[0] == S[1] && S[0] != '?')pat[1] = 0;
    for(int i = 0; i < N; i++){
        if(i > 1){
            if(S[i] != '?' && (S[i - 2] == S[i] || S[i - 1] == S[i]))pat[i] = 0;
        }
        if(S[i] == '?'){
            int cnt = 0;
            unordered_set<char> st;
            for(int j = -2; j <= 2; j++){
                if(!j)continue;
                int ni = i + j;
                if(ni < 0 || ni > N - 1)continue;
                if(S[ni] != '?')st.insert(S[ni]);
                else if(ni < i)cnt++;
            }
            pat[i] = 26 - st.size() - cnt;
        }
    }
    ll ans = 1;
    for(int i = 0; i < N; i++)ans = ans * pat[i] % mod;
    cout << ans << endl;
}