#include <bits/stdc++.h>

using namespace std;

ifstream in ("ciur.in");
ofstream out ("ciur.out");

int cnt, n, m;

bitset <1000000005> viz;
int primes[100000000];

int main() {
  in >> n;
  for(int i = 2; i <= n; i++) {
    if(!viz[i]) {
      primes[++m] = i;
    }
    for(int j = 1; j <= m && i * primes[j] <= n; j++)
      viz[i * primes[j]] = 1;
  }
  out << m;
  return 0;
}