#pragma region Macros
#include <bits/stdc++.h>
using namespace std;
template <class T> inline bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T> inline bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return 1;
    }
    return 0;
}
#ifdef DEBUG
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
    os << '{';
    for(int i = 0; i < (int)v.size(); i++) {
        if(i) { os << ','; }
        os << v[i];
    }
    os << '}';
    return os;
}
void debugg() { cerr << endl; }
template <class T, class... Args>
void debugg(const T &x, const Args &... args) {
    cerr << " " << x;
    debugg(args...);
}
#define debug(...)                                                             \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]: ", debugg(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif

struct Setup {
    Setup() {
        cin.tie(0);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(15);
    }
} __Setup;

using ll = long long;
#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
#define FOR(i, a, b) for(int i = (a); i < int(b); i++)
#define REP(i, n) FOR(i, 0, n)
const int INF = 1 << 30;
const ll LLINF = 1LL << 60;
constexpr int MOD = 1000000007;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

void Case(int i) { cout << "Case #" << i << ": "; }
int popcount(int x) { return __builtin_popcount(x); }
ll popcount(ll x) { return __builtin_popcountll(x); }
#pragma endregion Macros

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

int N;
string s;
mint dp[2][27][27];

int main() {
    cin >> N >> s;
    int now = 0, nxt = 1;
    dp[now][26][26] = 1;
    REP(i, N) {
        if(s[i] == '?') {
            REP(c1, 27) REP(c2, 27) {
                REP(c0, 26) {
                    if(c0 == c1 or c0 == c2) continue;
                    dp[nxt][c0][c1] += dp[now][c1][c2];
                }
            }
        } else {
            int c0 = s[i] - 'a';
            REP(c1, 27) REP(c2, 27) {
                if(c0 == c1 or c0 == c2) continue;
                dp[nxt][c0][c1] += dp[now][c1][c2];
            }
        }
        REP(c1, 27) REP(c2, 27) dp[now][c1][c2] = 0;
        swap(now, nxt);
    }

    mint ans = 0;
    REP(c1, 27) REP(c2, 27) ans += dp[now][c1][c2];
    cout << ans.val() << endl;
}