#include <bits/stdc++.h>
#define lglg long long
#define nmax 2000005
using namespace std;

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

bitset < nmax > is_prime;
vector < int > prime_numbers;
int n;
int nr_of_primes;

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

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