#include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <cmath>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <complex>
#include <string.h>
#include <unordered_set>
#include <unordered_map>
using namespace std;

#define endl '\n'
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define uniq(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef pair<int, int> P;
typedef unsigned int uint;
typedef unsigned long long ull;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};

const int inf = 1000000009;

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

P finite(ll k) {
    P p = P(0, 0);
    while (k % 2 == 0) {
	k /= 2;
	p.first++;
    }
    while (k % 5 == 0) {
	k /= 5;
	p.second++;
    }
    return (k == 1 ? p : P(-1, -1));
}

int main() {
    ll n, m;
    scanf("%lld%lld", &n, &m);
    ll g = gcd(n, m);
    n /= g;
    m /= g;
    P p = finite(m);
    if (p.first < 0) {
	printf("-1\n");
    } else {
	while (n % 10 == 0) n /= 10;
	int d = n % 10;
	if (p.second > 0) {
	    int a[4] = {6, 2, 4, 8};
	    d *= a[p.second%4];
	}
	if (p.first > 0) {
	    d *= 5;
	}
	while (d % 10 == 0) d /= 10;
	printf("%d\n", d%10);
    }
}