// includes
#include <cstdio>
#include <cstdint>
#include <iostream>
#include <iomanip>
#include <string>
#include <queue>
#include <stack>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <utility>
#include <functional>
#include <cmath>
#include <climits>
#include <bitset>
#include <list>
#include <random>
#include <boost/multiprecision/cpp_int.hpp>

// macros
#define ll long long int
#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 all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())

using namespace std;

//  types
typedef pair<int, int> P;
typedef pair<ll, int> Pl;
typedef pair<ll, ll> Pll;
typedef pair<double, double> Pd;
 
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1e9 + 7;

// solve
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;}


int main(int argc, char const* argv[])
{
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  namespace mp = boost::multiprecision;
  using Bint = mp::cpp_int;
  Bint N, M;
  string n, m;
  cin >> n >> m;
  N = Bint(n);
  M = Bint(m);
  Bint g = gcd(N, M);
  g = M / g;
  int t = 0;
  while(g % 2 == 0){
    g /= 2;
    t++;
  }
  int tt = 0;
  while(g % 5 == 0){
    g /= 5;
    tt++;
  }
  t = max(t, tt);
  if(g != 1)cout << -1 << endl;
  else{
    rep(i, t)N *= 10;
    Bint T = N / M;
    while(T % 10 == 0)T /= 10;
    cout << T % 10 << endl;
  }
	return 0;
}