#include<stdio.h>
int n;
bool v[2000099];
int main()
{ freopen("ciur.in","r",stdin);
  freopen("ciur.out","w",stdout);
  scanf("%d",&n);
  long long i,j,cnt=0;
  if(n>=2) cnt++;
  for(i=3;i<=n;i+=2)
  { if(v[i]==0)
     { cnt++;
       for(j=i*i;j<=n;j+=i)
		  v[j]=1;
	 }
  }	 
printf("%d",cnt);

	return 0;}