#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #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 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; templatebool chmax(T &a, const T &b) { if (abool chmin(T &a, const T &b) { if (b void cins(itr first,itr last){ for (auto i = first;i != last;i++){ cin >> (*i); } } template 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 pi; typedef pair P; typedef tuple tri; typedef pair point; typedef complex 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 a(n,26); 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); }