#include #pragma GCC optimize("Ofast") #define _GLIBCXX_DEBUG using namespace std; using std::cout; using std::cin; using std::endl; using ll=long long; using ld=long double; ll ILL=1167167167167167167; const int INF=2100000000; ll mod=998244353; #define rep(i,a) for (ll i=0;i using _pq = priority_queue, greater>; template ll LB(vector &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();} template ll UB(vector &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();} template bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;} template bool chmax(T &a,const T &b){if(a void So(vector &v) {sort(v.begin(),v.end());} template void Sore(vector &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});} void yneos(bool a){if(a) cout<<"Yes\n"; else cout<<"No\n";} int f(char a){ if(a=='?') return -1; return a-'a'; } //おちこんだりもしたけれど、私はげんきです。 int main() { ios::sync_with_stdio(false); cin.tie(nullptr); int N; cin>>N; string S; cin>>S; int va=26; vector dp(va*va); if(N==1){ if(S=="?") cout<<"26\n"; else cout<<"1\n"; return 0; } rep(i,va) rep(j,va){ if(i==j) continue; if(S[0]=='?'||f(S[0])==i){ if(S[1]=='?'||f(S[1])==j){ dp[i+j*va]=1; //cout<<"%"< dp2(va*va); if(true){ int a=f(S[l]); vector Y(va); rep(i,va) rep(j,va){ Y[j]+=dp[i+j*va]; Y[i]%=mod; } rep(i,va) rep(j,va){ if(i!=j&&a!=i){ if(a==-1||j==a) dp2[i+j*va]=(Y[i]-dp[j+i*va]); } } } /*else{ int a=f(S[l]); rep(i,va) rep(j,va){ if(a!=i&&a!=j){ dp2[j+a*va]=dp[i+j*va]; } } }*/ swap(dp,dp2); /*rep(i,va){ rep(j,va) cout<