func_code_string: #include <bits/stdc++.h>   using namespace std;   char s1[200010], s2[200010];   long long cal[200010][26], cal2[200010][26];   int main() {     int i, j, k, n;     long long qq = 0;     scanf( %d%s%s , &n, s1, s2);     for (i = 1; i <= n; i++) qq += (long long)i * i;     cal[0][s2[0] -  A ] = 1;     for (i = 1; i < n; i++) {       for (j = 0; j < 26; j++) cal[i][j] = cal[i - 1][j];       cal[i][s2[i] -  A ] += i + 1;     }     cal2[n - 1][s2[n - 1] -  A ] = 1;     for (i = n - 2; i >= 0; i--) {       for (j = 0; j < 26; j++) cal2[i][j] = cal2[i + 1][j];       cal2[i][s2[i] -  A ] += n - i;     }     long double res = 0;     for (i = 0; i < n; i++) {       res += (i + 1) * cal2[i][s1[i] -  A ];       if (i) res += (n - i) * cal[i - 1][s1[i] -  A ];     }     printf( %.12lf n , (double)(res / qq));     return 0;   }   