#include<stdio.h>
#include<stdlib.h>
int main()
{ 
	long n,i,j,contor;
	bool v[2000003];
	freopen("ciur.in", "rt", stdin);
	freopen("ciur.out", "wt", stdout);
	scanf("%ld",&n);
	for(i=2;i<=n;++i){   
		if(!v[i])   
		 {contor++;   
		  for(j=2;j*i<=n;++j) v[i*j]=1;}}
         
      printf("%ld", contor); return 0;
}