#include <stdio.h>
char v[2000001];
int n;
int cnt;

void ciur()
{
	for (int i=2;i<=n;++i)
		if (v[i]==0)
		{
			cnt++;
			for (int j=i*i;j<=n;)
			{
				v[j]=1;
				j+=i;
			}
		}
}



int main()
{
	freopen ("ciur.in","r",stdin);
	freopen ("ciur.out","w",stdout);
	scanf ("%d",&n);
	ciur();
	printf ("%d",cnt);
	return 0;
}