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;
class ProgramC
    {
        static void Main(string[] args)
        {
            
            //入力
            string[] input = Console.ReadLine().Split(' ');
            int a = int.Parse(input[0]);
            int b = int.Parse(input[1]);
            
            int min = 0;
            int max = 1250;
            int temp = 0;
            
            //二分探索法。
            while(max != min + 1)
            {
                //とりあえず真ん中の数でそれより大きいか小さいかを探す
                temp = (max + min) /2;
                
                //実際の金額を求めて、満たすなら最小、満たさないなら最大にする
                if((int)(temp * 0.08) < a || (int)(temp * 0.1) < b)
                    min = temp;
                else
                    max = temp;

            }
            
            //答え出力
            if((int)(max * 0.08) == a && (int)(max * 0.1) == b)
                Console.WriteLine(max);
            else
                Console.WriteLine("-1");

        } 
    }