#include<stdio.h>
long i,j,n,qq;
bool c[2000000];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%ld",&n);
	qq=n;
	for(i=2;i*i<=n;++i)
		if(!c[j])
		{
			for(j=i*i;j<=n;j+=i)
				{
					c[j]=true;
					qq--;
				}
		}
	
	printf("%ld",qq-1);
	return 0;
}