#include<stdio.h>
#include<math.h>
int main()
{ 
	long int n,i,j,v[2000000],contor=0;
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	scanf("%ld",&n);
	for(i=2;i<=(n/2);i++){
      for(j=2;(j*i)<=n;j++)
        {v[j*i]=1;}}
	for(i=2;i<=n;++i){ if(v[i]!=1) v[i]=0;}
    for(i=2;i<=n;i++)
      {if(v[i]==0)
		  contor++;} printf("%ld", contor); return 0;
}