#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

ll gcd(ll a,ll b) {
	ll tmp; 
	while(a) {
		tmp = b;
		b = a;
		a = tmp % a;
	} 
	return b;
}

ll n, m;

int main() {
//	freopen(".in", "r", stdin);
//	freopen(".out", "w", stdout);
	cin >> n >> m;
	ll t = gcd(n, m);
	n /= t; m /= t;
	if (m == 1) {
		while (n % 10 == 0) n /= 10;
		cout << n % 10;
		return 0;
	}
	ll _2 = 0, _5 = 0;
	while (m % 2 == 0) m /= 2, _2++;
	while (m % 5 == 0) m /= 5, _5++;
	if (m > 1) {
		cout << -1;
		return 0;
	}
	while (n % 10 == 0) n /= 10;
	n %= 10;
	while (_2--) {
		n *= 5;
		while (n % 10 == 0) n /= 10;
		n %= 10;
	}
	while (_5--) {
		n *= 2;
		while (n % 10 == 0) n /= 10;
		n %= 10;
	}
	cout << n;
	return 0;
}
/*


                __------__
              /~          ~\
             |    //^\\//^\|
           /~~\  ||  o| |o|:~\
          | |6   ||___|_|_||:|
           \__.  /      o  \/'
            |   (       O   )
   /~~~~\    `\  \         /
  | |~~\ |     )  ~------~`\
 /' |  | |   /     ____ /~~~)\
(_/'   | | |     /'    |    ( |
       | | |     \    /   __)/ \
       \  \ \      \/    /' \   `\
         \  \|\        /   | |\___|
           \ |  \____/     | |
           /^~>  \        _/ <
          |  |         \       \
          |  | \        \        \
          -^-\  \       |        )
               `\_______/^\______/
*/