import java.util.Scanner;


public class Main_yukicoder25 {

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

        long n = sc.nextLong();
        long m = sc.nextLong();

        long gcd = gcd(n, m);

        n /= gcd;
        m /= gcd;

        int cnt2 = 0;
        while (m % 2 == 0) {
        	cnt2++;
        	m /= 2;
        }
        int cnt5 = 0;
        while (m % 5 == 0) {
        	cnt5++;
        	m /= 5;
        }

        while (n % 10 == 0) {
        	n /= 10;
        }
        n %= 10;

        if (m != 1) {
        	System.out.println(-1);
        } else if (cnt2 == cnt5) {
        	System.out.println(n);
        } else if (cnt2 > cnt5) {
        	System.out.println(5);
        } else {
        	long tmp = 1;
        	for (int i = 0; i < cnt5 - cnt2; i++) {
        		tmp *= 2;
        	}
        	System.out.println(tmp * n % 10);
        }

        sc.close();
    }

	private static long gcd(long n, long m) {
		if (m == 0) {
			return n;
		} else {
			return gcd(m, n % m);
		}
	}
}