#include "bits/stdc++.h"
#define ALL(obj) (obj).begin(),(obj).end()
#define RALL(obj) (obj).rbegin(),(obj).rend()
#define REP(i, n) for(int i = 0; i < (int)(n); i++)
#define REPR(i, n) for(int i = (int)(n); i >= 0; i--)
#define FOR(i,n,m) for(int i = (int)(n); i < int(m); i++)
using namespace std;
typedef long long ll;
const int MOD = 1e9 + 7;
const int INF = MOD - 1;
const ll LLINF = 4e18;

//gcd
template<typename T>
T gcd(T a, T b) {
    return b ? gcd(b, a%b) : a;
}

int main() {
    ll n, m; cin >> n >> m;
    ll g = gcd(n, m);
    n /= g;
    m /= g;
    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 {
        if (cnt2 > cnt5) {
            puts("5");
        }
        else if (cnt5 > cnt2){
            switch ((cnt5 - cnt2) % 4) {
                case 0:
                    cout << n % 10 * 6 % 10 << endl;
                    break;
                case 1:
                    cout << n % 10 * 2 % 10 << endl;
                    break;
                case 2:
                    cout << n % 10 * 4 % 10 << endl;
                    break;
                case 3:
                    cout << n % 10 * 8 % 10 << endl;
                    break;
            }
        }
        else {
            while (n % 10 == 0) {
                n /= 10;
            }
            cout << n % 10 << endl;
        }
    }
    getchar(); getchar();
}