#include <iostream>
#include <fstream>

using namespace std;

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

int main()
{
    //1.
    int n = 0;
    int catePrime = 0;

    //2.
    fin >> n;

    //3.
    int v[n];

    for(int i = 2; i<=n; i++) v[i]= 0;

    v[0] = 1;
    v[1] = 1;

    for(int i = 1; i<=n; i++){
        if(v[i] == 0){
            for(int j = 2; j<=n/i; j++){
                v[i*j] = 1;
            }
        }
    }

    for(int i = 2; i<=n; i++){
        if(v[i] == 0){
            catePrime = catePrime + 1;
        }
    }

    //4.
    fout << catePrime << endl;
    return 0;
}