// clang-format off
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define mp make_pair
#define fst first
#define snd second
#define forn(i,n) for (int i = 0; i < int(n); i++)
#define forn1(i,n) for (int i = 1; i <= int(n); i++)
#define popcnt __builtin_popcountll
#define ffs __builtin_ffsll
#define ctz __builtin_ctzll
#define clz __builtin_clz
#define clzll __builtin_clzll
#define all(a) (a).begin(), (a).end()

using namespace std;
using namespace __gnu_pbds;

using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int,int>;
using pli = pair<ll,int>;
using pil = pair<int,ll>;
using pll = pair<ll,ll>;
template <typename T> using vec = vector<T>;
using vi = vec<int>;
using vl = vec<ll>;
template <typename T> using que = queue<T>;
template <typename T> using deq = deque<T>;
template <typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template <typename K, typename V> using ordered_map = tree<K, V, less<K>, rb_tree_tag, tree_order_statistics_node_update>;

template <typename T> T id(T b) {return b;};
template <typename T> void chmax(T &x, T y) {if (x < y) x = y;}
template <typename T> void chmin(T &x, T y) {if (x > y) x = y;}
template <typename S, typename K> bool contains(S &s, K k) { return s.find(k) != s.end(); }
template <typename T> bool getf(T flag, size_t i) { return (flag>>i) & 1; }
template <typename T> T setf(T flag, size_t i) { return flag | (T(1)<<i); }
template <typename T> T unsetf(T flag, size_t i) { return flag & ~(T(1)<<i); }
void fastio() { ios_base::sync_with_stdio(false); cin.tie(nullptr); }
constexpr ll TEN(int n) { if (n == 0) return 1LL; else return 10LL*TEN(n-1); }
// clang-format on

int main() {
    fastio();

    int n;
    string s;
    cin >> n >> s;

    const ll MOD = 998244353;

    auto idx = [](char c1, char c2) {
        return (c1 - 'a') * 27 + c2 - 'a';
    };

    vl dp(27 * 27);
    dp[27 * 27 - 1] = 1;
    forn(i, n) {
        vl temp(27 * 27);
        for (char c2 = 'a'; c2 <= 'z'; c2++) {
            if (s[i] == '?' or s[i] == c2) {
                for (char c0 = 'a'; c0 <= '{'; c0++) {
                    for (char c1 = 'a'; c1 <= '{'; c1++) {
                        if (c0 != c2 and c1 != c2) {
                            temp[idx(c1, c2)] = (temp[idx(c1, c2)] + dp[idx(c0, c1)]) % MOD;
                        }
                    }
                }
            }
        }
        dp = temp;
    }

    ll ans = 0;
    for (char c0 = 'a'; c0 <= '{'; c0++) {
        for (char c1 = 'a'; c1 <= '{'; c1++) {
            ans = (ans + dp[idx(c0, c1)]) % MOD;
        }
    }

    cout << ans << endl;

    return 0;
}