#include <fstream>
#include <cmath>

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

bool prime(int n)
{
    if (n % 2 == 0) return false;
    for (int i=3; i*i<=n; i+=2)
    {
        if (n % i == 0) return false;
    }
    return true;
}

main()
{
    int n,c=1;
    cin >> n;
    for (int i=3; i<=n; i+=2)
    {
        if (prime(i)) c++;
    }
    cout << c;
    cin.close();
    cout.close();
}