func_code_string: #include <bits/stdc++.h>   using namespace std;   const int mod = (int)1e9 + 7;   const int N_ = (int)2e6 + 2;   long long n;   char a[N_], b[N_];   double res;   long long T;   int main() {     scanf( %lld , &n);     scanf( %s , a + 1);     scanf( %s , b + 1);     for (char cur =  A ; cur <=  Z ; cur++) {       long long S = 0;       for (int i = 1; i <= n; i++) {         if (a[i] == cur) S += i;         if (b[i] == cur) res += S * (n - i + 1);       }       S = 0;       for (int i = 0; i <= n; i++) {         if (a[i] == cur) res += S * (n - i + 1);         if (b[i] == cur) S += i;       }     }     for (int i = 1; i <= n; i++) T += (n - i + 1) * (n - i + 1);     printf( %.9lf , res / T);     return 0;   }   