import java.util.*;

public class Main {
    public static void main(String[]  args) {
        Scanner sc = new Scanner(System.in);
        long n = sc.nextLong();
        long m = sc.nextLong();
        long g = gcd(n, m);
        n /= g;
        m /= g;
        long x = m;
        while(m % 10 == 0) {
            m /= 10;
        }
        int base = 1;
        while (x % 2 == 0) {
            x /= 2;
            base = 2;
        }
        while (x % 5 == 0) {
            x /= 5;
            base = 5;
        }
        if (x != 1) {
            System.out.println(-1);
            return;
        }
        if (m == 1) {
            while (n % 10 == 0) {
                n /= 10;
            }
            System.out.println(n % 10);
            return;
        }
        ArrayDeque<Integer> deq = new ArrayDeque<>();
        ArrayDeque<Integer> next = new ArrayDeque<>();
        long y = n;
        while(y > 0) {
            deq.addFirst((int)(y % 10));
            y /= 10;
        }
        while (m % base == 0) {
            int last = 0;
            boolean isFirst = true;
            while (deq.size() > 0 || last != 0) {
                int z = last * 10;
                if (deq.size() > 0) {
                    z += deq.poll();
                }
                if (!isFirst || z / base != 0) {
                    next.add(z / base);
                }
                last = z % base;
                isFirst = false;
            }
            ArrayDeque<Integer> tmp = next;
            next = deq;
            deq = tmp;
            m /= base;
        }
        while (deq.getLast() == 0) {
            deq.pollLast();
        }
        System.out.println(deq.getLast());
    }
    
    static long gcd(long x, long y) {
        if (x % y == 0) {
            return y;
        } else {
            return gcd(y, x % y);
        }
    }
}