#include <bits/stdc++.h>

#define REP(i, x, n) for(int i = x; i < (int)(n); i++)
#define rep(i, n) REP(i, 0, n)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define F first
#define S second
#define mp make_pair

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;

int main() {
  // ios_base::sync_with_stdio(false);
  ll N, M;
  cin >> N >> M;

  ll d = __gcd(N, M);
  N /= d;
  M /= d;

  int c2 = 0;
  int c5 = 0;
  while(M % 2 == 0) {
    c2++;
    M /= 2;
  }
  while(M % 5 == 0) {
    c5++;
    M /= 5;
  }

  if(M != 1) N = -1;
  else {
    while(N % 10 == 0) N /= 10;
    N %= 10;
    
    while(c2 > c5) {
      N = (N * 5) % 10;
      c5++;
    }
    while(c2 < c5) {
      N = (N * 2) % 10;
      c2++;
    }
  }
  
  cout << N << endl;
  
  return 0;
}