#include <iostream>
#include <string>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <vector>
#include <cmath>
#include <cstdlib>
#include <queue>
#include <stack>
#include <iomanip>

using namespace std;

#define REP(i, n) for(ll i = 0;i < n;i++)
#define REPR(i, n) for(ll i = n;i >= 0;i--)
#define FOR(i, m, n) for(ll i = m;i < n;i++)
#define FORR(i, m, n) for(ll i = m;i >= n;i--)
#define REPO(i, n) for(ll i = 1;i <= n;i++)
#define ll long long
#define INF (ll)1 << 60
#define MINF (-1 * INF)
#define ALL(n) n.begin(),n.end()
#define MOD 1000000007
#define P pair<ll, ll>

ll n, m, ans, a2 = 0, a5 = 0;

ll gcd(ll a, ll b) {
	return (b == 0 ? a : gcd(b, a % b));
}
int main() {
	cin >> n >> m;
	if (n % m == 0) {
		ll now = n / m;
		while (1) {
			if (now % 10 != 0) {
				cout << now % 10 << endl;
				return 0;
			}
			now /= 10;
		}
	}
	ll g = gcd(n, m);
	n /= g;
	m /= g;
	while (m % 2 == 0) {
		m /= 2;
		a2++;
	}
	while (m % 5 == 0) {
		m /= 5;
		a5++;
	}
	if (m != 1) {
		cout << -1 << endl;
		return 0;
	}
	if (a2 == a5) {
		while (1) {
			if (n % 10 != 0) {
				cout << n % 10 << endl;
				return 0;
			}
			n /= 10;
		}
	}
	n %= 10;
	REP(i, a2) {
		n *= 5;
		n %= 10;
	}
	REP(i, a5) {
		n *= 2;
		n %= 10;
	}
	cout << n << endl;
}