// 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>

// 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;}

using uint128 = __int128_t;

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(int 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);
  uint128 N, M;
  string n, m;
  cin >> n >> m;
  N = to_int128(n);
  M = to_int128(m);
  uint128 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;
    uint128 T = N / M;
    while(T % 10 == 0)T /= 10;
    cout << T % 10 << endl;
  }
	return 0;
}