// includes
#include <bits/stdc++.h>

// macros
#define pb emplace_back
#define mk make_pair
#define pq priority_queue
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define vrep(v, i) for(int i = 0; i < (v).size(); i++)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define FI first
#define SE second
#define bit(n) (1LL<<(n))
#define INT(n) int n; cin >> n;
#define LL(n) ll n; cin >> n;
#define DOUBLE(n) double n; cin >> n;
using namespace std;

template <class T>bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;}
template <class T>bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << p.first << " " << p.second; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << itr->first << ":" << itr->second; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}

//  types
using ll = long long int;
using P = pair<int, int>;
using Pli = pair<ll, int>;
using Pil = pair<int, ll>;
using Pll = pair<ll, ll>;
using Pdd = pair<double, double>;
using cd = complex<double>;

// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1e9 + 7;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};

// solve
ostream& operator<<(ostream& dest, __int128_t value) {
  ostream::sentry s(dest);
  if(s){
    __uint128_t tmp = value < 0 ? - value: value;
    char buf[128];
    char *d = end(buf);
    do{
      --d;
      *d = "0123456789"[tmp % 10];
      tmp /= 10;
    }while(tmp != 0);
    if(value < 0)--d, *d='-';
    int len = end(buf) - d;
    if(dest.rdbuf()->sputn(d, len) != len){
      dest.setstate(ios_base::badbit);
    }
  }
  return dest;
}

__int128_t to_int128(string s){
  __int128_t res = 0;
  for(size_t i = 0; i < s.size(); i++){
    res = res * 10 + (s[i] - '0');
  }
  return res;
}

template<typename T>
T gcd(T a, T b) {
  if(a > b)return gcd(b, a);
  if(a == 0)return b;
  return gcd(b % a, a);
}



int main(int argc, char const* argv[])
{
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(20);
  string s, t; cin >> s >> t;
  __int128_t n = to_int128(s);
  __int128_t m = to_int128(t);
  auto g = gcd(n, m);
  auto M = m / g;
  int two = 0, five = 0;
  while(M % 2 == 0){
    M /= 2;
    two++;
  }
  while(M % 5 == 0){
    M /= 5;
    five++;
  }
  if(M != 1){
    cout << -1 << endl;
    return 0;
  }
  n = n / g, m = m / g;
  if(two > five){
    rep(i, two - five)n *= 5;
  }else if(two < five){
    rep(i, five - two)n *= 2;
  }
  while(n){
    if(n % 10 != 0){
      cout << n % 10 << endl;
      return 0;
    }
    n /= 10;
  }
  return 0;
}