#include <fstream>
#define SMAX 2000010

std::ifstream fin("ciur.in");
std::ofstream fout("ciur.out");

int n, sol;
bool sieve[SMAX];

void erat() {
    for (int i = 2; i * i <= n; i++)
        if (!sieve[i])
            for (int j = i * i; j <= n; j += i)
                sieve[j] = true;

    sol = 1;
    for (int i = 3; i <= n; i += 2)
        if (!sieve[i])
            sol++;
}

int main() {
    fin >> n;
    erat();

    fout << sol << '\n';
    fout.close();
    return 0;
}