#include <iostream>
using namespace std;
template <typename T>
T uPow(T z,T n, T mod){
  T ans = 1;
  while(n != 0){
    if(n%2){
      ans*=z;
      if(mod)ans%=mod;
    }
    n >>= 1;
    z*=z;
    if(mod)z%=mod;
  }
  return ans;
}
template <typename T>
T gcd(T a,T b){
  if(a%b==0)return b;
  else return gcd(b,a%b);
}
int main(){
  long long A,B;cin>>A>>B;
  long long a = A/gcd(A,B);
  long long b = B/gcd(A,B);
  long long z = b;
  long long x = a;
  while(!(x%10)){
    x/=10;
  }
  x%=10;
  int t = 0;
  int f = 0;
  while(!(z%2)){
    t++;
    z/=2;
  }
  while(!(z%5)){
    f++;
    z/=5;
  }
  if(z!=1){
    cout << -1 << endl;
    return 0;
  }
  if(f==t){
    cout << 1*x << endl;
  }else if(f>t){
    cout << (uPow(2,(f-t),10)*(x%5))%10 << endl;
  }else{
    cout << 5 << endl;
  }
  
}