#include <fstream>
#include <math.h>
#include<iostream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
long long  a[2000001],n;
int nr=0, i, j;
int main() {
fin>>n;
for(i=2;i<=n;i++)a[i]=1;
for (i=2;i<=sqrt(n);i++)
 {if (a[i])
  {nr++;
     for(j=i*2;j<=n;j=j+i)
     {
         a[j]=0;
     }
  }
 }
fout<<nr;
return 0;
}