import std.algorithm, std.array, std.container, std.range, std.bitmanip;
import std.numeric, std.math, std.bigint, std.random;
import std.string, std.conv, std.stdio, std.typecons;

void main()
{
  auto n = readln.chomp.to!long;
  auto m = readln.chomp.to!long;

  reductFrac(n, m);

  if (n % m == 0) {
    writeln(lastWithoutZero(n / m));
  } else {
    writeln(lastDecimal(n, m));
  }
}

void reductFrac(ref long n, ref long m)
{
  auto g = gcd(n, m);
  n /= g;
  m /= g;
}

int lastWithoutZero(long n)
{
  while (n % 10 == 0) n /= 10;
  return n % 10;
}

int lastDecimal(long n, long m)
{
  auto r = n % 10;

  for (; m % 5 == 0; m /= 5)
    r = (r % 5) * 2;

  for (; m % 2 == 0; m /= 2)
    r = (r % 2 == 0 ? r / 2 : 5);

  return (m > 1 ? -1 : r).to!int;
}