#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  ull n, m;
  cin >> n >> m;
  ull g = gcd(n, m);
  n /= g, m /= g;
  int e2 = 0, e5 = 0;
  while (m % 2 == 0) m /= 2, e2++;
  while (m % 5 == 0) m /= 5, e5++;
  if (m != 1) {
    cout << -1 << endl;
  }
  else {
    int mn = min(e2, e5);
    e2 -= mn, e5 -= mn;
    string tmp = to_string(n);
    while (!tmp.empty() && tmp.back() == '0') tmp.pop_back();
    assert(!tmp.empty());
    ull ans = stoull(tmp) % 10;
    while (e2--) ans = (ans * 5) % 10;
    while (e5--) ans = (ans * 2) % 10;
    cout << ans << endl;
  }
  return 0;
}