#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  int s = 0;
  vector<int> np(n + 1);
  for (int i = 2; i < n + 1; ++i) {
    if (np[i]) continue;
    s += i;
    for (int j = i + i; j < n + 1; j += i) np[j] = 1;
  }
  cout << s << endl;
}