#include <iostream>
#include <iomanip>
#include <algorithm>
#include <assert.h>
#include <complex>
#include <utility>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <tuple>
#include <cmath>
#include <bitset>
#include <cctype>
#include <set>
#include <map>
#include <unordered_map>
#include <numeric>
#include <functional>
#define _overload3(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=a;i<b;++i)
#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define _rrep(i,a) rrepi(i,a,0)
#define rrepi(i,a,b) for(int i=a-1;i>=b;--i)
#define rrep(...) _overload3(__VA_ARGS__,rrepi,_rrep,)(__VA_ARGS__)
#define all(x) (x).begin(),(x).end()
#define PRINT(V) cout << V << "\n"
#define SORT(V) sort((V).begin(),(V).end())
#define RSORT(V) sort((V).rbegin(), (V).rend())
using namespace std;
using ll = long long;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
inline void Yes(bool condition){ if(condition) PRINT("Yes"); else PRINT("No"); }
template<class itr> void cins(itr first,itr last){
    for (auto i = first;i != last;i++){
        cin >> (*i);
    }
}
template<class itr> void array_output(itr start,itr goal){
    string ans = "",k = " ";
    for (auto i = start;i != goal;i++) ans += to_string(*i)+k;
    if (!ans.empty()) ans.pop_back();
    PRINT(ans);
}
ll gcd(ll a, ll b) {
    return a ? gcd(b%a,a) : b;
}

const int INF = 1e9;
const ll MOD = 1000000007;
const ll MOD2 = 998244353;
const ll MOD3 = 1e6;
const ll EPS = 1e-10;
int sgn(const double a){
    return (a < -EPS ? -1 : (a > EPS ? +1 : 0));
}
typedef pair<int,int> pi;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> tri;
typedef pair<double,double> point;
typedef complex<double> Point;
const ll MAX = 100005;
constexpr ll nx[4] = {-1,0,1,0};
constexpr ll ny[4] = {0,1,0,-1};

ll dp[50005][27][27] = {0};

int main(){
    int n;
    cin >> n;
    string s;
    cin >> s;
    vector<int> a(n,26);
    if (s.length() == 1){
        if (s[0] == '?'){
            PRINT(26);
        }
        else{
            PRINT(1);
        }
        return 0;
    }
    if (s.length() == 2){
        if (s[0] == s[1]){
            if (s[0] == '?'){
                PRINT(26*26-26);
            }
            else{
                PRINT(0);
            }
        }
        else{
            if (s[0] == '?' || s[1] == '?'){
                PRINT(25);
            }
            else{
                PRINT(1);
            }
        }
        return 0;
    }
    rep(i,n){
        if (s[i] == '?'){
            a[i] = -1;
        }
        else{
            a[i] = s[i]-'a';
        }
    }
    dp[0][26][26] = 1;
    rep(i,n){
        rep(j,27){
            rep(k,27){
                if (a[i] == -1){
                    rep(l,26){
                        if (j != l && k != l){
                            (dp[i+1][l][k] += dp[i][k][j])%=MOD2; 
                        }
                    }
                }
                else{
                    if (a[i] != j && a[i] != k){
                        (dp[i+1][a[i]][k] += dp[i][k][j])%=MOD2;
                    }
                }
            }
        }
    }
    ll ans = 0;
    rep(i,26){
        rep(j,26){
            (ans += dp[n][i][j])%=MOD2;
        }
    }
    PRINT(ans);
}