func_code_string: #include <bits/stdc++.h>   using namespace std;   long long aa[258], bb[258];   int main() {     ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0), cerr <<   ;     string a, b;     long long n;     cin >> n;     cin >> a >> b;     long double s = 0;     for (int i = 1; i <= n; ++i)       aa[b[i - 1]] += i,           s += (n - i + 1) * (aa[a[i - 1]] + bb[b[i - 1]]) * 1.0 / n,           bb[a[i - 1]] += i;     long double l = s * 1.0 / (n + 1) / (2 * n + 1);     l *= 6.0;     cout.precision(9);     cout << fixed << l;   }   