#include <iostream>
#include <fstream>
#include <bitset>

using namespace std;

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

bitset <2000001> ciur;

int main() {
  int n, prime, i, j;
  fin >> n;
  for ( i = 2; i * i <= n; i++ )
    if ( ciur[i] == 0 )
      for ( j = i * i; j <= n; j += i )
        ciur[j] = 1;
  prime = 0;
  for ( i = 2; i <= n; i++ )
    if ( ciur[i] == 0 )
      prime++;
  fout << prime;
  return 0;
}