#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);
  //system("PAUSE");
  return 0;
}