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;
using System.Text;
using System.Threading.Tasks;

namespace AtCoders {
	class Program {
		static void Main(string[] args) {

			var inputArray = new string[3];
			inputArray = Console.ReadLine().Split(' ');

			// 不正な入力は処理しない
			if (inputArray.Length != 2) {
				Console.WriteLine("invalid input");
				return;
			}

			// 入力値セット
			var A = long.Parse(inputArray[0]);
			var B = long.Parse(inputArray[1]);

			// Aの消費税になる最大の税抜き金額=A+1円の消費税の金額になる最小の税抜き金額-1
			var MinA = CalcMinZeinuki(A, 0.08);
			var MaxA = CalcMinZeinuki(A + 1, 0.08) - 1;

			var MinB = CalcMinZeinuki(B,  0.1);
			var MaxB = CalcMinZeinuki(B + 1, 0.1) - 1;

			int ans;

			if(MinA <= MaxB & MinB <= MaxA) {
				ans = Math.Max(MinA, MinB);
			}
			else {
				ans = -1;
			}
			//Console.WriteLine($"8% {MinA},{MaxA}  10%{MinB},{MaxB}");
			Console.WriteLine(ans);

		}

		private static int CalcMinZeinuki(long A,double tax) {
			
			return (int)Math.Ceiling(A / tax);

		}
	}
}