#include <fstream>

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

const int m = 2e6+5;

bool v[m];

int main() {
    int n;
    cin >> n;
    v[0] = 1;
    v[1] = 1;
    int cnt = 0;
    for (int i = 2; i <= n; ++i) {
        if (v[i] == 0) { 
            ++cnt;
            for (int j = 2 * i; j <= n; j += i)
                v[j] = 1;
        }
    }
    cout << cnt;

    return 0;
}