#include<bits/stdc++.h>
using namespace std;

int main()
{
  bool is_prime[1000000];fill(is_prime,is_prime+1000000,true);
  int count_prime[1000000];fill(count_prime,count_prime+1000000,0);
  is_prime[0]=false,is_prime[1]=false;
  for(int i=2;i<1000000;i++)
  {
    count_prime[i]=count_prime[i-1]+is_prime[i];
    if(!is_prime[i])continue;
    for(int j=i*2;j<1000000;j+=i)is_prime[j]=false;
  }
  int n;
  while(cin>>n)printf("%d\n",count_prime[n]);
}
