#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int c[2000001];
int main()
{
    int n, nr, p, m;
    f >> n;
    nr = n - 1;
    for(p = 2; p * p <= n; p++)
        if(c[p] == 0)
            for( m = p * p; m <= n; m += p){
                c[m] = 1;
                nr--;
            }
    g << nr;


    return 0;
}