#include <fstream>
#include <cmath>
#include <bitset>
#include <random>
#include <iostream>
#include <time.h>
#define MAX 2000003
#define NR 12312311

using namespace std;

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

int primes[148950];
int K = 0;

bool isprime(int val) {
    for(int i = 0; primes[i]*primes[i] <= val; i++) {
        if(val%primes[i] == 0)
            return false;
    }
    return true;
}

int n,k;
int main() {
    in >> n;
    primes[K++] = 2;
    for(int i = 3; i <= n; i++)
        if(isprime(i))
            primes[K++] = i;
    out << K;
    return 0;
}