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

using namespace std;
ifstream fin("ciur.in");
ofstream fout("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()
{
    fin>>n;
    ciur();
    fout<<nr_of_primes;

    return 0;
}