CF1062D Fun with Integers

思路：

找规律。

实现：

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main()
{
    ll n;
    while (cin >> n)
    {
        ll cnt = 0;
        for (int i = 2; i * i <= n; i++)
        {
            ll tmp = n / i;
            cnt += (i + 1 + tmp) * (tmp - i) / 2;
            cnt += (tmp - i + 1) * i;
        }
        cout << (cnt << 2) << endl; 
    }
    return 0;
}