#include <cstdio>

long v[500000];

int main() 
{
	long n,i,j,pr=0;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%ld", &n);
	for(i=2; i<=n; ++i)
	{
		if(not v[i])
		{
			pr++;
			for(j=2; j<=n/i; ++j)
				v[i*j]=1;
		}
	}
	printf("%ld",pr);
	return 0;
}