#include <iostream>
#include <fstream>

using namespace std;

const int MAX = 2000000;

char p[MAX + 1];

fstream f("ciur.in", ios::in), g("ciur.out", ios::out);

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