Problem:
Score : 300 points

Problem Statement

Find the price of a product before tax such that, when the consumption tax rate is 8 percent and 10 percent, the amount of consumption tax levied on it is A yen and B yen, respectively. (Yen is the currency of Japan.)

Here, the price before tax must be a positive integer, and the amount of consumption tax is rounded down to the nearest integer.

If multiple prices satisfy the condition, print the lowest such price; if no price satisfies the condition, print -1.

Constraints

1 \leq A \leq B \leq 100

A and B are integers.

Input

Input is given from Standard Input in the following format:

A B

Output

If there is a price that satisfies the condition, print an integer representing the lowest such price; otherwise, print -1.

Sample Input 1

2 2

Sample Output 1

25

If the price of a product before tax is 25 yen, the amount of consumption tax levied on it is:

When the consumption tax rate is 8 percent: \lfloor 25 \times 0.08 \rfloor = \lfloor 2 \rfloor = 2 yen.

When the consumption tax rate is 10 percent: \lfloor 25 \times 0.1 \rfloor = \lfloor 2.5 \rfloor = 2 yen.

Thus, the price of 25 yen satisfies the condition. There are other possible prices, such as 26 yen, but print the minimum such price, 25.

Sample Input 2

8 10

Sample Output 2

100

If the price of a product before tax is 100 yen, the amount of consumption tax levied on it is:

When the consumption tax rate is 8 percent: \lfloor 100 \times 0.08 \rfloor = 8 yen.

When the consumption tax rate is 10 percent: \lfloor 100 \times 0.1 \rfloor = 10 yen.

Sample Input 3

19 99

Sample Output 3

-1

There is no price before tax satisfying this condition, so print -1.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

class Abc158c
{
    static int a, b;

    static void Solve()
    {
        var xa_min = ((a * 100) % 8) == 0 ? a * 100 / 8 : a * 100 / 8 + 1;
        var xa_max = (((a + 1) * 100) % 8) == 0 ? (a + 1) * 100 / 8 : (a + 1) * 100 / 8 + 1;
        var xb_min = b * 10;
        var xb_max = (b + 1) * 10;

        var answer = -1;
        for(var i = xa_min; i < xa_max; ++i) {
            if(xb_min <= i && i < xb_max) {
                answer = i;
                break;
            }
        }

        Console.WriteLine(answer);
    }

    static void Scan()
    {
        var buf = Console.ReadLine().Split().ToList().ConvertAll(int.Parse);
        a = buf.ElementAt(0);
        b = buf.ElementAt(1);
    }

    static void Main()
    {
        Scan();
        Solve();
    }
}