#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;

map<ull,int> factorize(ull x){
  map<ull,int> ret;
  ull d, q;
  while(x>=4 && x%2==0){ret[2]++; x/=2;}
  d = 3; q = x/d;
  while(q>=d){
    if(x%d==0){ ret[d]++; x=q; }else{ d+=2; }
    q=x/d;
  }
  ret[x]++;
  return ret;
}

ll mod_pow(ll x, ll n, ll mod){
  ll res = 1;
  while(n>0){
    if(n&1) res = res*x%mod;
    x = x*x%mod;
    n >>= 1;
  }
  return res;
}

int main(){
  ull N, M;
  cin >> N;
  cin >> M;

  int mx;
  map<ull,int> res1 = factorize(N);
  map<ull,int> res2 = factorize(M);

  if(res2.count(2) == 0 && res2.count(5) == 0){
    cout << -1 << endl;
    return 0;
  }
  FOR(it,res2){
    mx = max(res1[it->first], res2[it->first]);
    res1[it->first]-=mx;
    res2[it->first]-=mx;
  }

  FOR(it,res2){
    if(it->second == 0) continue;
    if(it->first != 2 && it->first != 5){
      cout << -1 << endl;
      return 0;
    }
  }
  
  mx = max(res2[2],res2[5]);
  res1[2]+=mx;
  res1[5]+=mx;
  res1[2]-=res2[2];
  res1[5]-=res2[5];
  mx = max(res1[2], res1[5]);
  res1[2]-=mx;
  res1[5]-=mx;

  
  ull ret = 1;
  FOR(it,res1){
    ret *= mod_pow(it->first, it->second, 10);
    ret %= 10;
  }
  cout << ret << endl;
  
  return 0;
}