#include <iostream>
#include <fstream>
#define nmax 2000001
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int main()
{int n,i,j,ct=0;
 bool a[nmax]={0};
 fin>>n;
 a[2]=1;
 for (i=3;i<=n;i=i+2) a[i]=1;
 for (i=3;i*i<=n;i=i+2)
       if (a[i]==1)
            for (j=3*i;j<=n;j=j+2*i)
                     a[j]=0;
 for (i=1;i<=n;i++)
     if (a[i]==1) ct++;
 fout<<ct;
 fin.close();
 fout.close();
    return 0;
}