#include <iostream>
using namespace std;

bool ciur[50000001];
int main() {
    int n, counter = 0;
    cin >> n;
    for (int d = 2; d <= n; ++d) {
        if (ciur[d] == false) {
            for (int i = 2; i <= n / d; ++i) {
                ciur[i * d] = true;
            }
            ++counter;
        }
    }
    cout << counter;
    return 0;
}