#include<stdio.h>
long i,j,n,qq;
const long N = 1<<21;//1 shiftat la stanga cu 21 de pozitii = 2 la 21
bool c[N];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%ld",&n);
	for(i=2;i*i<=n;++i)
		if(!c[i])
		{
			for(j=i*i;j<=n;j+=i)
				c[j]=true;
		}
	for(i=2;i<=n;i++)
		if(!c[i])
			qq++;
	printf("%ld",qq);
	return 0;
}