import java.util.Scanner;

public class Yuki025 {
    public static void main(String[] args) {
        Yuki025 p = new Yuki025();

    }

    Yuki025() {
        Scanner scanner = new Scanner(System.in);
        long numerator = scanner.nextLong();
        long denominator = scanner.nextLong();
        System.out.println(solve(numerator, denominator));
    }

    long gcd(long a, long b) {
        while (b > 0) {
            long c = a % b;
            a = b;
            b = c;
        }
        return a;
    }

    long pow(int v, int p, long init) {
        long ans = init % 10;
        for (int i = 0; i < p; i++) {
            ans *= v;
            ans %= 10;
        }
        return ans;
    }

    int getLastNonZero(long v) {
        long ans = v;
        while (ans % 10 == 0) {
            ans /= 10;
        }
        return (int) ans % 10;
    }

    int solve(long _numerator, long _denominator) {
        final long gcd = gcd(_numerator, _denominator);
        long numerator = _numerator / gcd;
        long denominator = _denominator / gcd;

        long num = denominator;
        if (num == 1) {
            return getLastNonZero(numerator);
        }
        int[] div = new int[6];
        int[] divs = {2, 5};
        for (int d : divs) {
            while (num > 1) {
                if (num % d > 0) {
                    break;
                }
                div[d]++;
                num /= d;
            }
        }
        if (num > 1) {
            return -1;
        }
        final int diff = Math.max(div[5], div[2]) - Math.min(div[5], div[2]);
        if (div[5] == div[2]) {
            return (int) (numerator % 10);
        } else if (div[5] < div[2]) {
            return (int) pow(5, diff, numerator);
        } else {
            return (int) pow(2, diff, numerator);
        }
    }

}