#include <fstream>
#include <bits/stdc++.h>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");

int ciur(int n){
 int i, j;
 vector <bool> a(n + 5, 0);
 int nr_prime = 1;
  for(i = 4; i <= n; i += 2)
    a[i] = 1;
  for(i = 3; i <= n; i += 2)
    {
      if(a[i] == 0)
        {
        //  cout << i << '\n';
          nr_prime++;
          for(j = i; j <= n / i; j++)
            a[j * i] = 1;
        }
    }
  return nr_prime;
}

int main(){
  int n;
  cin >> n;
  cout << ciur(n);
  return 0;
}