#include<stdio.h>
#include<math.h>
using namespace std;
int n,i,nr,k,v[2000010];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	nr=0;
	for(i=2;i<=n;i++)
	{
		if(v[i]==0)
		{
			nr=nr+1;
			for(k=2;k*i<=n;k++)
			{
				v[k*i]=1;
			}
		}
	}
	printf("%d\n",nr);
	
	return 0;
}