#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

using namespace std;

int main() {
  int n;
  cin >> n;
  vector<bool> pr(n + 1, true);
  int ans = 0;
  for (int i = 2; i <= n; i++) {
    if (pr[i]) {
      ans += i;
      for (int j = i * 2; j <= n; j += i) {
        pr[j] = false;
      }
    }
  }
  cout << ans << endl;
}