#include <stdio.h>
#include <string.h>

int n,prim[2000100],i,nr,j;

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

  scanf("%d", &n);
  memset(prim,1,sizeof(prim));

  for (i=2;i<=n;++i)
       if (prim[i])
       {
	nr++;
	for (j=i+i;j<=n;j+=i)
	     prim[j]=0;
       }
  printf("%d", nr);
  return 0;
}