#include <fstream>
using namespace std;

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

int result[4000001];

int ciur(int N) {
    int counter = 0;
    for (int i = 2; i * i <= N; ++i) {
        if (result[i] == 0) {
            for (int d = i + i; d <= N; d += i) {
                result[d] = -1;
            }
        }
    }
    for (int i = 2; i <= N; ++i) {
        if (result[i] == 0) {
            ++counter;
        }
    }
    return counter;
}

int main() {
    int N;
    fin >> N;
    fout << ciur(N);
    return 0;
}