#include <iostream>
#include <fstream>

using namespace std;

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

bool v[2000003];
//int prim[100000];

int n,k;

int main() {

    in >> n;

    for(int i = 2; i <= n; i++) {

        if(!v[i]) {

            //prim[k++] = i;
            k++;
            int mult = i*i;

            while(mult < 2000003) {

                v[mult] = 1;
                mult += i;

            }

        }

    }

    out << k;

    return 0;

}