/*
https://infoarena.ro/problema/ciur
*/
#include <fstream>

using namespace std;

const int NMAX = 2e6;

bool c[NMAX+1];

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int n;
    in >> n;
    c[0] = c[1] = true;
    for (int i = 2; i * i <= n; i++)
    {
        if (!c[i])
        {
            for (int m = i * i; m <= n; m += i)
            {
                c[m] = true;
            }
        }
    }
    int nr = 0;
    for (int i = 2; i <= n; i++)
    {
        if (!c[i])
        {
            nr++;
        }
    }
    out << nr << "\n";
    in.close();
    out.close();
    return 0;
}