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