#include <iostream>
#include <stdio.h>

using namespace std;

int main()
{
    freopen("input.txt", "r", stdin);
    long long a, b;
    cin >> a >> b;
    //cout << "ASDWQWQ";
    long long mas[a + 1];
    mas[b] = 1;
    swap(a, b);
    //cout << "SSSSADAS";
    for (long long i = a + 1; i <= b; i++)
    {
        if (i % 2 == 0 && i / 2 >= a)
        {
            mas[i] = min(mas[i - 1], mas[i / 2]) + 1;
        }
        else
        {
            mas[i] = mas[i - 1] + 1;
        }
    }
    //cout << "SAD";
    long long k = mas[b] - 1, last = b;
   //ans[0] = a;
  // cout << mas[b] << endl;
    for (long long i = b - 1; i >= a; i--)
    {
        if (mas[i] == k && (i + 1 == last || i * 2 == last))
        {
            if (i + 1 == last)
                {
                    cout << "-1" << endl;
                    last = i;
                }
            else
                {
                    cout << ":2" << endl;
                    last = i;
                }
            //ans[k] = i;
            k--;
        }
    }


}