#include #include using namespace std; using namespace atcoder; constexpr long long INF_LL = 2000000000000000000LL; constexpr int INF = 2000000000; constexpr long long MOD = 1000000007; #define all(x) x.begin(), x.end() #define REP(i, a, b) for(int i = a; i < b; i++) #define rep(i, n) REP(i, 0, n) typedef long long ll; typedef pair P; typedef vector vi; typedef vector vvi; typedef vector

vp; typedef vector vl; int dx[4] = {0, -1, 0, 1}; int dy[4] = {1, 0, -1, 0}; int sign[2] = {1, -1}; template bool chmax(T &a, T b) { if(a < b) { a = b; return 1; } return 0; } template bool chmin(T &a, T b) { if(a > b) { a = b; return 1; } return 0; } ll modpow(ll a, ll b, ll m) { if(b == 0) return 1; ll t = modpow(a, b / 2, m); if(b & 1) { return (t * t % m) * a % m; } else { return t * t % m; } } struct edge { int to; ll cost; edge(int t, ll c) { to = t, cost = c; } }; typedef vector> graph; using mint = modint998244353; // constexpr int MAX_COM = 2001; // mint fac[MAX_COM], ifac[MAX_COM]; // void initfac() { // fac[0] = ifac[0] = 1; // REP(i, 1, MAX_COM) fac[i] = i * fac[i - 1]; // REP(i, 1, MAX_COM) ifac[i] = 1 / fac[i]; // } // mint nCr(int n, int r){ // if(r < 0 || n < r) return 0; // return fac[n] * ifac[n - r] * ifac[r]; // } // typedef ll S; // S op(S x, S y){ return min(x, y); } // S e(){ return INF_LL; } // int mapping(int f, int x){ return f ^ x; } // int composition(int f, int x){ return f ^ x; } // int id(){ return 0; } mint dp[50001][27][27]; int main(){ cin.tie(0); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(16); int n; string s; cin >> n >> s; dp[0][26][26] = 1; rep(i, n){ rep(j, 27){ rep(k, 27){ if(s[i] == '?'){ rep(c, 26){ if(c != j && c != k){ dp[i + 1][k][c] += dp[i][j][k]; } } }else{ if(s[i] - 'a' != j && s[i] - 'a' != k){ dp[i + 1][k][s[i] - 'a'] += dp[i][j][k]; } } } } } mint ans = 0; rep(i, 27) rep(j, 27) ans += dp[n][i][j]; cout << ans.val() << endl; }