#include <bits/stdc++.h>
using namespace std;

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

template <typename T, typename Compare = less<T>>
T &chmin(T &l, T r, Compare &&f = less<T>()) { return l = min(l, r, f); }
template <typename T, typename Compare = less<T>>
T &chmax(T &l, T r, Compare &&f = less<T>()) { return l = max(l, r, f); }

#include <atcoder/modint>
using mint = atcoder::modint998244353;

int main() {
    int n; cin >> n;
    string s; cin >> s;

    for (int i = 0; i < n - 1; ++i) {
        if (s[i] == '?' || s[i + 1] == '?') {
            continue;
        }

        if (s[i] == s[i + 1]) {
            cout << 0 << endl;
            return 0;
        }
    }

    for (int i = 0; i < n - 2; ++i) {
        if (s[i] == '?' || s[i + 2] == '?') {
            continue;
        }

        if (s[i] == s[i + 2]) {
            cout << 0 << endl;
            return 0;
        }
    }

    mint ans = 1;
    for (int i = 0; i < n; ++i) {
        if (s[i] != '?') {
            continue;
        }

        int l = i - max(0, i - 2);
        int r = min(n, i + 3) - (i + 1);

        for (int j = i + 1; j < min(n, i + 3); ++j) {
            r -= s[j] == '?';
        }

        ans *= 26 - (l + r);
    }

    cout << ans.val() << endl;
}