#include <iostream>
#include <fstream>
#include <vector>
#include <bitset>
#define ll long long
#define nmax 2000005


using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

bitset <nmax> is_prime;
vector <int> prime_nr;
ll nr_of_primes=0;
ll n;


void ciur() {
   for(ll i=2;i<=n;i++){
        if(is_prime[i]==0){
            for(ll j=i*i;j<=n;j+=i){
                is_prime[j]=1;
        }
    prime_nr.push_back(i);
    nr_of_primes++;
     }
    }
   }

int main()
{ f>>n;
  ciur();
  g<<nr_of_primes;
  return 0;
}