#pragma GCC optimize ("Ofast") #include using namespace std; #define MD (998244353U) struct modint{ static unsigned md; unsigned val; modint(){ val=0; } modint(int a){ val = ord(a); } modint(unsigned a){ val = ord(a); } modint(long long a){ val = ord(a); } modint(unsigned long long a){ val = ord(a); } void setmod(unsigned m){ md = m; } unsigned ord(unsigned a){ return a%md; } unsigned ord(int a){ a %= (int)md; if(a < 0){ a += md; } return a; } unsigned ord(unsigned long long a){ return a%md; } unsigned ord(long long a){ a %= (int)md; if(a < 0){ a += md; } return a; } unsigned get(){ return val; } inline modint &operator++(){ val++; if(val >= md){ val -= md; } return *this; } inline modint &operator--(){ if(val == 0){ val = md - 1; } else{ --val; } return *this; } inline modint operator++(int a){ modint res(*this); val++; if(val >= md){ val -= md; } return res; } inline modint operator--(int a){ modint res(*this); if(val == 0){ val = md - 1; } else{ --val; } return res; } modint &operator+=(modint a){ val += a.val; if(val >= md){ val -= md; } return *this; } modint &operator-=(modint a){ if(val < a.val){ val = val + md - a.val; } else{ val -= a.val; } return *this; } modint &operator*=(modint a){ val = ((unsigned long long)val*a.val)%md; return *this; } modint &operator/=(modint a){ return *this *= a.inverse(); } modint operator+(modint a){ return modint(*this)+=a; } modint operator-(modint a){ return modint(*this)-=a; } modint operator*(modint a){ return modint(*this)*=a; } modint operator/(modint a){ return modint(*this)/=a; } modint operator+(int a){ return modint(*this)+=modint(a); } modint operator-(int a){ return modint(*this)-=modint(a); } modint operator*(int a){ return modint(*this)*=modint(a); } modint operator/(int a){ return modint(*this)/=modint(a); } modint operator+(long long a){ return modint(*this)+=modint(a); } modint operator-(long long a){ return modint(*this)-=modint(a); } modint operator*(long long a){ return modint(*this)*=modint(a); } modint operator/(long long a){ return modint(*this)/=modint(a); } modint operator-(void){ modint res; if(val){ res.val=md-val; } else{ res.val=0; } return res; } operator bool(void){ return val!=0; } operator int(void){ return get(); } operator long long(void){ return get(); } modint inverse(){ int a = val; int b = md; int u = 1; int v = 0; int t; modint res; while(b){ t = a / b; a -= t * b; swap(a, b); u -= t * v; swap(u, v); } if(u < 0){ u += md; } res.val = u; return res; } modint pw(unsigned long long b){ modint a(*this); modint res; res.val = 1; while(b){ if(b&1){ res *= a; } b >>= 1; a *= a; } return res; } bool operator==(int a){ return ord(a)==val; } bool operator!=(int a){ return ord(a)!=val; } } ; unsigned modint::md; modint operator+(int a, modint b){ return modint(a)+=b; } modint operator-(int a, modint b){ return modint(a)-=b; } modint operator*(int a, modint b){ return modint(a)*=b; } modint operator/(int a, modint b){ return modint(a)/=b; } modint operator+(long long a, modint b){ return modint(a)+=b; } modint operator-(long long a, modint b){ return modint(a)-=b; } modint operator*(long long a, modint b){ return modint(a)*=b; } modint operator/(long long a, modint b){ return modint(a)/=b; } inline int my_getchar(){ static char buf[1048576]; static int s = 1048576; static int e = 1048576; if(s == e && e == 1048576){ e = fread(buf, 1, 1048576, stdin); s = 0; } if(s == e){ return EOF; } return buf[s++]; } inline void rd(int &x){ int k; int m=0; x=0; for(;;){ k = my_getchar(); if(k=='-'){ m=1; break; } if('0'<=k&&k<='9'){ x=k-'0'; break; } } for(;;){ k = my_getchar(); if(k<'0'||k>'9'){ break; } x=x*10+k-'0'; } if(m){ x=-x; } } inline void rd(char &c){ int i; for(;;){ i = my_getchar(); if(i!=' '&&i!='\n'&&i!='\r'&&i!='\t'&&i!=EOF){ break; } } c = i; } inline int rd(char c[]){ int i; int sz = 0; for(;;){ i = my_getchar(); if(i!=' '&&i!='\n'&&i!='\r'&&i!='\t'&&i!=EOF){ break; } } c[sz++] = i; for(;;){ i = my_getchar(); if(i==' '||i=='\n'||i=='\r'||i=='\t'||i==EOF){ break; } c[sz++] = i; } c[sz]='\0'; return sz; } struct MY_WRITER{ char buf[1048576]; int s; int e; MY_WRITER(){ s = 0; e = 1048576; } ~MY_WRITER(){ if(s){ fwrite(buf, 1, s, stdout); } } } ; MY_WRITER MY_WRITER_VAR; void my_putchar(int a){ if(MY_WRITER_VAR.s == MY_WRITER_VAR.e){ fwrite(MY_WRITER_VAR.buf, 1, MY_WRITER_VAR.s, stdout); MY_WRITER_VAR.s = 0; } MY_WRITER_VAR.buf[MY_WRITER_VAR.s++] = a; } inline void wt_L(char a){ my_putchar(a); } inline void wt_L(int x){ int s=0; int m=0; char f[10]; if(x<0){ m=1; x=-x; } while(x){ f[s++]=x%10; x/=10; } if(!s){ f[s++]=0; } if(m){ my_putchar('-'); } while(s--){ my_putchar(f[s]+'0'); } } inline void wt_L(modint x){ int i; i = (int)x; wt_L(i); } int N; char S[50000+10]; int s[50000+10]; modint dp[28][28]; modint ndp[28][28]; int main(){ int i, j; { modint x; x.setmod(MD); } rd(N); rd(S); for(i=(0);i<(N);i++){ if('a' <= S[i] && S[i] <= 'z'){ s[i] = S[i] - 'a'; } else{ s[i] = -1; } } for(i=('a');i<('z'+1);i++){ int j; if(S[0] != '?' && S[0] != i){ continue; } for(j=('a');j<('z' + 1);j++){ if(S[1] != '?' && S[1] != j){ continue; } if(i == j){ continue; } ++dp[i-'a'][j-'a']; } } for(i=(2);i<(N);i++){ int j; for(j=('a');j<('z' + 1);j++){ int k; for(k=('a');k<('z' + 1);k++){ ndp[j-'a'][k-'a'] = 0; } } for(j=('a');j<('z' + 1);j++){ int k; if(S[i] != '?' && S[i] != j){ continue; } for(k=('a');k<('z' + 1);k++){ int lk; if(k == j){ continue; } for(lk=('a');lk<('z'+1);lk++){ if(lk == j){ continue; } if(lk == k){ continue; } ndp[k-'a'][j-'a'] += dp[lk-'a'][k-'a']; } } } for(j=('a');j<('z' + 1);j++){ int k; for(k=('a');k<('z' + 1);k++){ dp[j-'a'][k-'a'] = ndp[j-'a'][k-'a']; } } } modint res; res = 0; for(j=('a');j<('z' + 1);j++){ int k; for(k=('a');k<('z' + 1);k++){ res += dp[j-'a'][k-'a']; } } wt_L(res); wt_L('\n'); return 0; } // cLay version 20210405-1 // --- original code --- // //no-unlocked // #define MD 998244353 // int N; // char S[5d4+10]; // int s[5d4+10]; // modint dp[28][28]; // modint ndp[28][28]; // { // rd(N, S); // rep(i, N){ // if('a' <= S[i] <= 'z') s[i] = S[i] - 'a'; // else s[i] = -1; // } // rep(i, 'a', 'z'+1){ // if(S[0] != '?' && S[0] != i) continue; // rep(j, 'a', 'z' + 1){ // if(S[1] != '?' && S[1] != j) continue; // if(i == j) continue; // ++dp[i-'a'][j-'a']; // } // } // rep(i, 2, N){ // rep(j, 'a', 'z' + 1){ // rep(k, 'a', 'z' + 1) ndp[j-'a'][k-'a'] = 0; // } // rep(j, 'a', 'z' + 1){ // if(S[i] != '?' && S[i] != j) continue; // rep(k, 'a', 'z' + 1){ // if(k == j) continue; // rep(lk, 'a', 'z'+1){ // if(lk == j) continue; // if(lk == k) continue; // ndp[k-'a'][j-'a'] += dp[lk-'a'][k-'a']; // } // } // } // rep(j, 'a', 'z' + 1){ // rep(k, 'a', 'z' + 1) dp[j-'a'][k-'a'] = ndp[j-'a'][k-'a']; // } // } // modint res; // res = 0; // rep(j, 'a', 'z' + 1){ // rep(k, 'a', 'z' + 1) res += dp[j-'a'][k-'a']; // } // wt(res); // }