#include <stdio.h>
int n,nr;
char ok[2000009];
int main()
{ 
  int n,i,j,nr;
  
  freopen("ciur.in","r",stdin);
  freopen("ciur.out","w",stdout);
  scanf("%d",&n);
  for (i=2;i<=n;i++) ok[i]=0;nr=0;
  for (i=2;i<=n;i++) 
	if (ok[i]=0) {nr++; for (j=i+i;j<= n; j+=i)  ok[j] = 1; }  
 printf("%d",nr);

return 0;}