#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

ll gcd(ll a, ll b) {
	if (b == 0) return a;
	return gcd(b, a % b);
}

int main() {
	ll n, m;
	cin >> n >> m;
	
	ll g = gcd(n, m);
	n /= g; m /= g;
	
	if (n % m == 0) {
		stringstream ss;
		ss << n / m;
		string str = ss.str();
		int ans;
		REP(i, str.size()) if (str[i] != '0') ans = str[i] - '0';
		cout << ans << endl;
		return 0;
	}
	
	int cnt2 = 0, cnt5 = 0;
	while (m % 2 == 0) cnt2++, m /= 2;
	while (m % 5 == 0) cnt5++, m /= 5;
	
	if (m != 1) puts("-1");
	else {
		n %= 10;
	
		REP(i, cnt5) n = n * 2 % 10;
		
		REP(i, cnt2) n = n * 5 % 10;
		
		cout << n << endl;
	}
	return 0;
}