import java.util.Scanner;

public class Yukicoder25 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong();
		long M = sc.nextLong();

		long div;
		while ((div = gcd(N, M)) != 1) {
			N /= div;
			M /= div;
		}
		while (M % 10L == 0L) M /= 10;

		N = N % 10 == 0 ? 1 : N % 10;
		while (M % 5L == 0L) {
			M /= 5;
			N = N * 2 % 10;
		}
		while (M % 2L == 0L) {
			M /= 2;
			N = 5;
		}
		N = M == 1 ? N : -1;
		System.out.println(N);

	}

	static long gcd(long a, long b) {
		long c, tmp;

		if (a < b) {
			tmp = a;
			a = b;
			b = tmp;
		}

		while (b != 0) {
			c = a % b;
			a = b;
			b = c;
		}
		return a;
	}
}