func_code_string: #include <bits/stdc++.h>   using namespace std;   long long int sf[26][200005], tf[26][200005];   int main() {     long long int n, i, j;     cin >> n;     double ans = 0.0;     string s, t;     cin >> s >> t;     for (i = 0; i < n; ++i) {       sf[s[i] -  A ][i] += (i + 1);       tf[t[i] -  A ][i] += (i + 1);       if (i)         for (j = 0; j < 26; ++j) {           sf[j][i] += sf[j][i - 1];           tf[j][i] += tf[j][i - 1];         }       ans = ans + (n - i) * ((i ? sf[t[i] -  A ][i - 1] : 0) + tf[s[i] -  A ][i]);     }     ans = (6 * ans) / (n * (n + 1) * (2 * n + 1));     cout << fixed << setprecision(8) << ans;     return 0;   }   