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: Wrong Answer)

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

namespace AtCorder
{
    public static class Program
    {
        static public void Main(string[] args)
        {
            //int cnt = int.Parse(Console.ReadLine());
            double[] input=  Console.ReadLine().Split(' ').Select(double.Parse).ToArray();
            double per8 = input[0] * 12.5;
            double per10 = input[1] * 10;

            double[] array8 = new double[10];
            double[] array10 = new double[10];
            array8[0] = per8;
            array10[0] = per10;

            for (int num = 1; num <= 9; num++)
            {
                array8[num] = array8[num - 1] + 1.25;
                array10[num] = array10[num - 1] + 1;
            }

            double ans = 0;
            bool flg = false;
            foreach (double tax8 in array8)
            {
                foreach (double tax10 in array10)
                {
                    if (Math.Truncate(tax8) == Math.Truncate(tax10))
                    {
                        ans = Math.Truncate(tax8);
                        flg = true;
                        break;
                    }
                }
                if (flg)
                {
                    break;
                }
                
            }
            if (ans == 0)
            {
                Console.WriteLine((-1).ToString());
            }
            else
            {
                Console.WriteLine(ans.ToString());
            }
                        
        }
    }
}