#include <fstream>

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

bool v[2000000 + 1];
int n, i, j, nr;

int main()
{
        f >> n;
        for (i = 1; i < n; i++)
                v[i] = 1;

        for (i = 1; i < n; i++)
                if (v[i]) {
                        nr++;
                        for (j = i + i + 1; j < n; j += i + 1)
                                v[j] = 0;
                }

        g << nr;

        return 0;
}