#include <bitset>
#include <fstream>
using namespace std;

bitset<2000001> e;

void Ciur() {
    int i, j;
    e[0] = e[1] = 1;
    for (i = 2; i * i <= 2000000; i++)
        if (!e[i])
            for (j = 2; j * i <= 2000000; j++)
                e[i * j] = 1;
}

int prime = 0;

int main() {
    int x, i;
    ifstream f("ciur.in");
    f >> x;
    f.close();

    Ciur();

    for (i = 2; i < x; i++)
        if (!e[i])
            prime++;

    ofstream g("ciur.out");
    g << prime;
    g.close();
    return 0;
}