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

ifstream f("ciur.in");
ofstream g("ciur.out");

int v[50000001];

int main() {
    int N, nr = 1;
    f >> N;
    if (N == 0 || N == 1) {
        cout << 0;
        return 0;
    }
    for (int i = 2; i * i <= N; ++i) {
        if (v[i] == 0) {
            for (int j = i; j <= (N / i); ++j) {
                v[i * j] = 1;
            }
        }
    }
    for (int i = 3; i <= N; i += 2) {
        if (v[i] == 0) {
            nr++;
        }
    }
    g << nr;
    return 0;
}