#include<cstdio>
#define Nmax 2000005
using namespace std;
bool a[Nmax];
int n,nr=0;
int main()
{freopen("ciur.in","rt",stdin);
 freopen("ciur.out","wt",stdout);
 scanf("%d",&n);
 for(register int i=2;i<=n;++i)
	 if(!a[i])
	   {nr++;for(register int j=i;j<=n;j+=i) a[j]=true;}
 printf("%d\n",nr);
 return 0;
}