#include<iostream>
#include<fstream>
using namespace std;
int n,a[2000005],x,i,j;
ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{ 
	f >> n;
	
for ( i=2;i<=n;i++)
	a[i]=1;

for(i = 2; i<=n;i++)
	if(a[i])
	{ x++;	
		for( j=i+i; j<=n;j+=i)
		 a[j]=0;
	}
g<<x<<"\n";
return 0;
}