#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = (ll)(1e+9) + 7;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef long double ld;
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;
typedef pair<ld, ld> LDP;
typedef unsigned long long ul;
ul gcd(ul a, ul b) {
	if (a < b)swap(a, b);
	while (b) {
		ul r = a % b; a = b; b = r;
	}
	return a;
}
int main() {
	ul n, m; cin >> n >> m;
	ul d = gcd(n, m);
	n /= d; m /= d;
	int c[2] = {};
	while (m % 2 == 0) {
		m /= 2; c[0]++;
	}
	while (m % 5 == 0) {
		m /= 5; c[1]++;
	}
	while (n % 10 == 0)n /= 10;
	if (m > 1) {
		cout << -1 << endl;
	}
	else {
		if (c[0] > c[1]) {
			cout << 5 << endl;
		}
		else if (c[0] == c[1]) {
			cout << n % 10 << endl;
		}
		else {
			int nex = n % 10;
			rep(i, c[1] - c[0]) {
				nex = 2 * nex % 10;
			}
			cout << nex << endl;
		}
	}
	return 0;
}