import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import static java.lang.System.in;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        int A = Integer.parseInt(reader.readLine());
        int answer = -1;
        for (int i = 1; i <= A - 7; i++) {
            if (A % i == 7 && A / i == 1) {
                answer=i;
            }
        }
        System.out.println(answer);
    }

}