#include<iostream.h>
int i,c,n,j;
char v[2000001];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(i=2;i<=n;i++)
		if(!v[i])
		{
			v[i]=1;
			c++;
			for(j=2*i;j<=n;j+=i)
				v[j]=1;
		}
	printf("%d",c);
	return 0;
}