#include<stdio.h>
#include<math.h>
using namespace std;
int n,nr;
char a[2000005];
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	int i,j;
    for(i=2;i<=n;++i)
	{
		if(a[i]==0)
			{
				++nr;
			  for(j=i+i;j<=n;j+=i)
				a[j]=1;
		}
	}
	
	printf("%d\n",nr);
	//for(i=2;i<=n;i++)
		//if(a[i]==0)
		//printf("%d ",i);
	return 0;
}