#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
#define rep(i,s,e) for(int (i) = (s);(i) <= (e);(i)++)
#define all(x) x.begin(),x.end()

int N;

vector<int> pri(101010,-1);

int main(){
  cin >> N;
  int ans = 0;
  rep(i,2,N){
    if(pri[i] == -1){
      pri[i] = 1;
      ans += i;
      for(int j = i + i;j <= N;j += i){
        pri[j] = 0;
      }
    }
  }

  cout << ans << endl;
}