#include <iostream>
#include <fstream>
#include <iomanip>
#include <cmath>
#include <string>

#define LIM 2000005
using namespace std;

bool viz[LIM];

int main() {

    int n, cnt = 0;

    cin >> n;

    for(int i = 2; i <= n; i++) {
        if(!viz[i]) {
            cnt++;
            if(i <= n / i) {
                for(int j = i * i; j <= n; j += i) {
                    viz[j] = true;
                }
            }
        }
    }

    cout << cnt << "\n";

    return 0;
}