#include<iostream>
#include<fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out("ciur.out");
char a[2000003];
int main ()
{    int n,i,j,k;
     in>>n;k=1;
     
for (i=2;i<=n;i++)
     a[i]=0;     

for (i=3;i<=n;i=i+2)
{	if (!a[i]) 
     {  k++;
  		for (j=i+i;j<=n;j=j+i)
			a[j]=1;
} 
}

    
		out<<k;
return 0;
}