#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
long long primeNumber(long long x) {
  bool fire = true;
  for(int i = 2; i <= sqrt(x); i++) {
    if(x % i == 0) {
      fire = false;
    }
  }
  return fire;
}
int main() {
  int N; cin >> N;
  long long ans = 0;
  for(long long a = 2; a <= N; a++) {
    if(primeNumber(a)) {
      ans += a;
    }
  }
  cout << ans << endl;
}