#include<iostream>
#include<fstream>
#define IMAX 2000000
using namespace std;
int a[IMAX];
int main()
{
ifstream f ("ciur.in");
ofstream o ("ciur.out");

int n,i,j,nrsol=0;

f>>n;
for(i=2;i<=n;i++)
      if(a[i]==0)
           { nrsol ++;
                for(j=i+i;j<=n;j=j+i)
                                    a[j]=1;
           }


cout<<nrsol<<"\n";



return 0;}