#include <fstream>
#include <iostream>
#include <bitset>

using namespace std;

bitset<2000001> prim;
int n, prime, d, m;
ifstream fi("ciur.in");
ofstream fo("ciur.out");

int main () {
    fi >> n;
    prim.set();
    for (d = 2; d <= n; d++)
        if (prim[d]) {
            if (n / d > d)
                for (m = d * d; m <= n; m += d)
                    prim[m] = 0;
            prime++;
        }
    fo << prime;
    return 0;
}