#include <stdio.h>

using namespace std;
int prim[2000000];
int n,res=0;

int main()
{
  freopen("ciur.in","r",stdin);
  freopen("ciur.out","w",stdout);

 scanf("%d",&n);

 for(int i=1;i<=n;i++)
  prim[i]=1;

  for(int i=2;i<=n;i++)
   if(prim[i])
     {
       res++;
         for(int j=2*i;j<=n;j+=i)
            prim[j]=0;
     }

printf("%d",res);
return 0;
}