#include <iostream>
#include <fstream>

using namespace std;

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

int prim[2000005] , i , n , cnt = 0;

int main()
{
    prim[1] = 1;
    for (int i = 2 ; i <= 2000000 ; i++)
    {
        if (prim[i] == 0)
        {
           for (int j = 2 * i ; j <= 2000000 ; j = j + i)
              prim[j] = 1;
        }
    }

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