#include <iostream>
using namespace std;

char sieve[2000001];

int main () {
  freopen("ciur.in","r",stdin);
  freopen("ciur.out","w",stdout);

  long long n; cin >> n;
  long long k = 0;
  for(long long i = 2; i <= n; i++)
    sieve[i] = 1;
  for(long long i = 2; i <= n; i++)
  if(sieve[i]) {
    k++;
    for(long long j = i + i; j <= n; j += i)
      sieve[j] = 0;
  }
  cout << k;
}