#include <bits/stdc++.h>

#define FOR(i, a, b) for (ll i = (a); i < (b); i++)
#define RFOR(i, a, b) for (ll i = (b)-1; i >= (a); i--)
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define rep1(i, n) for (ll i = 1; i <= (n); i++)
#define rrep(i, n) for (ll i = (n)-1; i >= 0; i--)

#define pb push_back
#define mp make_pair
#define fst first
#define snd second
#define show(x) cout << #x << " = " << x << endl
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define pii pair<int, int>
#define vi vector<int>

using namespace std;
template <class S, class T>
ostream& operator<<(ostream& o, const pair<S, T>& p)
{
    return o << "(" << p.first << "," << p.second << ")";
}
template <class T>
ostream& operator<<(ostream& o, const vector<T>& vc)
{
    o << "sz = " << vc.size() << endl
      << "[";
    for (const T& v : vc)
        o << v << ",";
    o << "]";
    return o;
}
using ll = long long;
constexpr ll MOD = 1000000007;

ll gcd(ll n, ll m)
{
    if (n % m == 0) {
        return m;
    } else if (m % n == 0) {
        return n;
    } else if (n > m) {
        return gcd(n % m, m);
    } else {
        return gcd(m % n, n);
    }
}

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

    while (M % 10 == 0) {
        M /= 10;
    }
    if (M % 2 == 0) {
        while (M % 2 == 0) {
            M /= 2;
        }
        if (M != 1) {
            cout << -1 << endl;
            return 0;
        }
        cout << 5 << endl;
    } else if (M % 5 == 0) {
        N = N % 5;
        while (M % 5 == 0) {
            M /= 5;
            N = (N * 2) % 10;
        }
        if (M != 1) {
            cout << -1 << endl;
            return 0;
        }
        cout << N << endl;
    } else if (M == 1) {
        while (N % 10 == 0) {
            N /= 10;
        }
        cout << N % 10 << endl;
    } else {
        cout << -1 << endl;
    }


    return 0;
}