#include <iostream>
#include <fstream>

using namespace std;

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

int n , cnt;

bool prim[2000005];

int main()
{
    f >> n;
    for (int i = 2 ; i <= n ; i++)
    {
        if (prim[i] == 0)
        {
            cnt++;
           for (int j = 2 * i ; j <= n ; j = j + i)
              prim[j] = 1;
        }
    }
    g << cnt;
    return 0;
}