//#include <iostream>
#include <fstream>
using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");
int eprim(int n)
{
    for(int i = 2; i * i <= n; i++)
    {
         if(n % i == 0)
             return 0;

    }
    return 1;
}

int main()
{
    int n, cont = 0;
    cin >> n;
    for(int i = 2;i<=n;i++)
        {
            if(eprim(i))
                cont++;
        }
    cout << cont;
    return 0;

}