#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

bool isPrime(const vector<long long> &a, const long long &N) {
    for (int i = 0; i < a.size() && a[i]*a[i]<=N; i++) {
        if (N%a[i] == 0) {
            return false;
        }
    }
    return true;
}

vector<long long> primeList(long long N) {
    vector<long long> a;
    a.push_back(2);
    for (int i = 3; i <=N; i+=2) {
        if (isPrime(a, i)) {
            a.push_back(i);
        }
    }
    return a;
}

int main() {
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    int n;
    cin>>n;
    vector <long long> a = primeList(n);
    cout<<a.size();
    return 0;
}