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

const int NMAX = 2000005;

bitset<NMAX> prim;

int main() {
    int n;

    ifstream cin ("ciur.in");
    ofstream cout ("ciur.out"); 
    cin >> n;
    
    for (int i = 3; i * i <= n; i+= 2) {
        if (prim[i]) {
            continue;
        }

        for (int j = i * i; j <= n; j+= 2 * i) {
            prim[j] = 1;
        }
    }

    cout << (n + 1) / 2 - prim.count();

    return 0;
}