#include<stdio.h>   
#include<stdlib.h>   
long n,nr;   
bool v[2000001];   
int main()   
  {   
   freopen("ciur.in","rt",stdin);   
   freopen("ciur.out","wt",stdout);   
   scanf("%ld",&n);   
   for(long i=2;i<=n;++i)   
      if(!v[i])   
        {nr++;   
         for(long j=2;j*i<=n;++j) v[i*j]=1;   
        }   
  printf("%ld",nr);     
  return 0;   
}