#include <fstream>

using namespace std;

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

const int NMAX = 2e6;

int n, s;
int ciur[NMAX];

void Ciur_Eratosthenes() {
    ciur[0] = ciur[1] = 1;
    for (int i = 2; i <= NMAX; i++)
        if (!ciur[i])
            for (int j = i + i; j <= NMAX; j += i)
                ciur[j] = 1;
}

int main() {
    Ciur_Eratosthenes();
    fin >> n;
    for (int i = 0; i <= n; i++) {
        s += (!ciur[i] ? 1 : 0);
    }
    fout << s;
    return 0;
}