#include <iostream>
using namespace std;

int main(){
  int n;
  cin >> n;

  if(n==1){cout << 0 << endl;return 0;}
  int sum=2;
  for(int i=3;i<=n;i++){
    bool judge=true;
    for(int j=2;j<i;j++){
      if(i%j==0){judge=false;break;}
    }
    if(judge==true)sum+=i;
  }
  cout << sum << endl;
  return 0;
}