#include <bits/stdc++.h>
#define rep(i, a) for (int i = 0; i < (a); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define repr(i, a) for (int i = (a) - 1; i >= 0; i--)
#define repr2(i, a, b) for (int i = (b) - 1; i >= (a); i--)
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 1e9 + 7;

map<ll, ll> primefactor(ll n) {
    map<ll, ll> res;
    for (ll i = 2; i * i <= n; i++) {
        while (n % i == 0) {
            res[i]++;
            n /= i;
        }
    }
    if (n != 1) res[n]++;
    return res;
}

ll modpow(ll a, ll b) {
	ll res = 1;
	while (b > 0) {
		if (b & 1) (res *= a) %= 10;
		(a *= a) %= 10;
		b >>= 1;
	}
	return res;
}

ll power(ll n, ll m) {
	ll res = 1;
	rep (i, m) res *= n;
	return res;
}

int main() {
	ll N, M;
	cin >> N >> M;
	ll g = __gcd(N, M);
	N /= g;
	M /= g;

	auto pf = primefactor(M);
	auto pf2 = primefactor(N);

	bool any = false;
	for (auto p : pf) {
		any |= p.first != 2 && p.first != 5;
	}

	if (any) {
		cout << -1 << endl;
		return 0;
	}

	int x = pf[2];
	int y = pf[5];

	N /= power(10, min(pf2[2], pf2[5]));

	if (x == y) {
		cout << N % 10 << endl;
	} else if (x < y) {
		ll ans = N % 10 * modpow(2, max(x, y) - x) % 10;
		cout << ans << endl;
	} else if (x > y) {
		ll ans = N % 10 * modpow(5, max(x, y) - y) % 10;
		cout << ans << endl;
	}

    return 0;
}