#include<iostream>
#include<cstdio>
using namespace std;

typedef long long int ll;

#define rrep(i, m, n) for(int i=m; i<n; i++)
#define  rep(i, n)    for(int i=0; i<n; i++)

ll n, m;
ll g;
ll cnt[2];
ll mmin, mmax;
ll res;
ll x;

ll gcd(ll a, ll b);

int main()
{
  cin >> n >> m;

  g = gcd(n, m);
  n /= g;
  m /= g;

  ll tmp = m;
  while(m%2==0){ m/=2;  cnt[0]+=1; }
  while(m%5==0){ m/=5;  cnt[1]+=1; }

  if(m!=1){
    cout << "-1" << endl;
    return 0;
  }

  m = tmp;
  if(n%m==0){
    while(n%10==0) n/=10;
    cout << n%10 << endl;
    return 0;
  }

  if(cnt[0] > cnt[1]) x = 5;
  if(cnt[0] < cnt[1]) x = 2;

  mmax = max(cnt[0], cnt[1]);
  mmin = min(cnt[0], cnt[1]);

  res = n;
  rep(i, mmax-mmin) res = (res * x) % 10;

  cout << res % 10 << endl;

  return 0;
}

ll gcd(ll a, ll b)
{
  ll tmp;

  while(b){
    tmp = a;
    a = b;
    b = tmp%b;
  }

  return a;
}