#include<stdio.h>

int ciur[2000001],n,nr;

int main(){
	
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	scanf("%d",&n);
	
	for(int i=2;i<=n;++i)
		for(int j=i+i;j<=n;j+=i)
			ciur[j]=1;
	
	for (int i=2;i<=n;++i)
		if(!ciur[i])
			nr++;
	
	printf("%d\n",nr);
	
	return 0;
}