#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP(i,(int)(n)-1,0)
#define REP(i,s,e) for (i = s; i <= e; i++)
#define rep(i,n) REP(i,0,(int)(n)-1)
#define INF 100000000

typedef long long ll;
typedef unsigned long long ull;

int main() {
    int i;
    ull n, m;
    cin >> n >> m;
    ll d = __gcd(n,m);
    n /= d;
    m /= d;
    while (n % 10 == 0) n /= 10;
    while (m % 10 == 0) m /= 10;
    n %= 10;
    while (m % 2 == 0 || m % 5 == 0) {
        if (m % 2 == 0) {
            n = n * 5 % 10;
            m /= 2;
        }
        if (m % 5 == 0) {
            n = n * 2 % 10;
            m /= 5;
        }
    }
    if (m == 1)
        cout << n << endl;
    else
        cout << -1 << endl;
    return 0;
}