#include <iostream>
#include <fstream>

using namespace std;

int sir[2000002];

int main()
{
  int n,i,j,rez=0;

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

  ciurin>>n;

  for (i=2;i<=n;++i)
    sir[i]=1;

  for (i=2;i<=n;++i)
    if (sir[i]==1){
      ++rez;
      for (j=i+i;j<=n;j+=i)
        sir[j]=0;
    }

  ciurout<<rez;

    return 0;
}