#include <bits/stdc++.h>

using namespace std;

template<typename T> inline T gcd(T a, T b) {
  return __gcd(a, b);
}

template<typename T> inline T lcm(T a, T b) {
  return a / gcd(a, b) * b;
}

template<typename T> inline T floor(T a, T b) {
  return a / b * b <= a ? a / b : a / b - 1;
}

template<typename T> inline T ceil(T a, T b) {
  return floor(a + b - 1, b);
}

template<typename T> inline T round(T a, T b) {
  return floor(a + b / 2);
}

template<typename T> inline T mod(T a, T b) {
  return a - floor(a, b) * b;
}

template<typename T> inline T factorial(T n) {
  return n <= 1 ? 1 : factorial(n - 1) * n;
}

int main() {
  long long n, m;
  cin >> n >> m;
  auto g = gcd(n, m);
  n /= g;
  m /= g;
  while (n % 10 == 0) n /= 10;
  n %= 10;
  while (m != 1) {
    n *= 10;
    g = gcd(n, m);
    if (g == 1) {
      cout << -1 << endl;
      return 0;
    }
    n /= g;
    m /= g;
    n %= 10;
  }
  cout << n << endl;
}