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

namespace AtCoder
{
	class Program
	{
		static void Main(string[] args)
		{
			var n = ReadLineIntSplit();
			int a = n[0];
			int b = n[1];

			int i = 1;
			while (true)
			{
				if (i > 1250) break;
				if ((int)(i * 0.08) == a && (int)(i * 0.1) == b) break;
				i++;
			}

			if (i < 1250)
			Console.WriteLine(i);
			else Console.WriteLine("-1");

		}

		public static int nCm(int n, int m)
		{
			if (n == 0) return 0;
			if (m == 0) return 1;
			return n * nCm(n - 1, m - 1) / m;
		}

		public static string ReadLine()
		{
			return Console.ReadLine();
		}

		public static int ReadLineInt()
		{
			return int.Parse(ReadLine());
		}

		public static string[] ReadLineStringSplit(char s = ' ')
		{
			return ReadLine().Split(s).ToArray();
		}

		public static int[] ReadLineIntSplit(char s = ' ')
		{
			return ReadLine().Split(s).Select(x => int.Parse(x)).ToArray();
		}

		public static long[] ReadLineLongSplit(char s = ' ')
		{
			return ReadLine().Split(s).Select(x => long.Parse(x)).ToArray();
		}
	}
}