#include <cstdio>
char a[2000003];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	int i,n,sol=0;
	scanf("%d",&n);
	for (i=2;i<=n;++i)
		if (!a[i])
		{
			sol++;
			for (int j=2*i;j<=n;j+=i)
				a[j]=1;
		}
	printf("%d\n",sol);
	return 0;
}