using namespace std;
#include<fstream>
#include<iostream>
#include<cstdio>
bool a[2000002];
int main ()
{ int i,j,n,s=1;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
	for(i=3;i*i<=n;i=i+2)
	   if(a[i]==0)
		{  s++;
			for(j=i*i;j<=n;j=i+j)
			   a[j]=1;
		}
	printf("%d",s);
	return 0;
}