#include <iostream>
#include <fstream>

using namespace std;

const int NMAX = 2000005;

char prim[NMAX];

int main() {
    int n;

    ifstream cin ("ciur.in");
    ofstream cout ("ciur.out"); 
    cin >> n;

    int  sol = 0;
    
    for (int i = 2; i <= n; i++) {
        if (prim[i]) {
            continue;
        }

        sol++;

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

    cout << sol;

    return 0;
}