#include <bits/stdc++.h>

using namespace std;
int main() {
  long int N;
  cin >> N;
  long int count=0;
  long int K;
  for (long int i=1;i<=N;i++){
    K=N/i;
    count+=i*K*(K+1)/2;
  }
  cout << count <<endl;
return 0;
}