import java.util.Scanner;

/**
 * yukicoder no.25
 * @author scache
 *
 */
public class FiniteDecimal {
	public static void main(String[] args) {
		FiniteDecimal p = new FiniteDecimal();
	}

	public FiniteDecimal() {
		Scanner sc = new Scanner(System.in);
		long n = sc.nextLong();
		long m = sc.nextLong();
		

//		System.out.println(solve(1024L*1024*1024*1024*1024*1024*4, 625L*625*625*625*625*625));
		System.out.println(solve(n, m));
	
	}

	public int solve(long n, long m) {
		long g = gcd(n, m);
		m /= g;
		n /= g;
		
		while(n%10 == 0)
			n /= 10;
		
		long res = n;
		
		while(m%10==0)
			m /= 10;
		
		res %= 1000000000000000000L;
		while(m%2==0){
			res *= 5;
			m /= 2;

			res %= 1000000000000000000L;
		}
		
		
		while(m%5==0){
			res *= 2;
			m /= 5;

			res %= 1000000000000000000L;
		}
			
		if(m==1)
			return (int)res%10;
		else
			return -1;
	}
	
	private long gcd(long a, long b){
		if(b==0)
			return a;
		else
			return gcd(b, a%b);
	}
}