#include<stdio.h>
#include<math.h>
int prim(int x)
{
	int d;
	if(x==0||x==1||x%2==0 && x!=2) return 0;
	else d=sqrt(x);
	for(int i=3;i<=d;i=i+2) 
		if(x%i==0) return 0;
	return 1;
}
int main()
{
	int N,nr=0;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&N);
	for(int i=2;i<=N;i++) 
		if(prim(i)) nr++;
	printf("%d",nr);
	return 0;
}