#include <iostream>
using namespace std;
typedef long long ll;
const ll MAXN=1e7+7;
ll n,sum;
int main()
{
	cin>>n;
	sum=(1+n)*n/2;
	for(int i=2;i<=n;i++) sum+=(i+n/i*i)*(n/i)/2;
	cout<<sum<<endl;
	return 0;
}