#include <iostream>
#include <fstream>

using namespace std;
int n , a , nr , b;
bool v [2000001];

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

    fin >> n ;
    for (a=2;a<=n;a=a+1){
        if (v[a] == 0) {
            nr=nr + 1;
            for (b=a+a;b<=n;b=b+a){
            v[b] = 1;}
        }
    }
    fout << nr;
    fin.close();
    fout.close();
    return 0;

}