#include <fstream>
#include <iostream>
#include <string.h>
#define NMAX 2000005
using  namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
  int n, primeCounter = 0;
  char ciur[NMAX];
  memset(ciur,'1',sizeof(ciur));
  fin>>n;
  for(int i = 2; i * i <= n; i++)
  {
    if(ciur[i] == '1')
    {
      for(int j = i * i; j <= n; j+=i)
        ciur[j] = '0';
      primeCounter++;
    }
  }
  fout<<primeCounter;
  return 0;
}