func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int a, b;     cin >> a;     if (a == 1) {       cout <<  1 ;       return 0;     }     if (a == 2) {       cout <<  13 ;       return 0;     }     long long sol = 1;     sol += 1LL * 6 * a * (a + 1) / 2;     sol += 1LL * 6 * ((a - 2) * (a - 1) / 2 - 1);     cout << sol <<   n ;     return 0;   }   