func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int n;     cin >> n;     int prev = 0;     int ans = 0;     for (int i = 1; i <= n; i++) {       ans += (n - i) * (i - 1) + i;       prev = i;     }     cout << ans;   }   