//
//  main.cpp
//  ciur lui erastostene
//
//  Created by Florian Marcu on 4/8/21.
//

#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main() {

    int prim[2000000];
    int n, i;
    fin >> n;

    for (i = 2; i <= n; i++)
        prim[i] = 1;

    int k = 0, j;
    for (i = 2; i <= n; i++)
        if(prim[i])
        {
            k++;
            for (j = i+i; j <= n; j+=i)
                 prim[j] = 0;

        }
    fout << k << "\n";





        




    return 0;
}