#include<stdio.h>
char v[2000001];
int main()
{
  freopen("ciur.in","r", stdin);
  freopen("ciur.out","w",stdout);
  long i,n,j,k,l,m,cnt=0;
  scanf("%ld",&n);
  for(i=1;i<=n;i++)
  v[i]=1;
  for(i=2;i<=n;i++)
   if(v[i])
   {
	cnt++;
	for(j=i+i;j<=n;j+=i)
	 {
	  v[j]=0;
	 }
   }
 /* for(i=2;i<=n;i++)
  {
   if(v[i]==1)g<<i<<" ";
 }
*/
printf("%ld",cnt);
return 0;
}