#include <iostream>
#include <fstream>

using namespace std;

ifstream f ("ciur.in");
ofstream g ("ciur.out");

int i, j, nr, n, A[1001];

int main()
{
    f >> n;

    for (i = 2; i <= n; i++)
    {
        if (A[i] == 0)
        {
            nr++;

            for (j = i + i; j <= n; j = j + i)
            {
                A[j] = 1;
            }
        }
    }

    g << nr;

         return 0;
}