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 Ruby (2.3.3) (judge verdict: Accepted)

# 消費税率が 8 %のとき A 円、10 ％のとき B 円の消費税が課されるような商品の税抜き価格を求めてください。
# ただし、税抜き価格は正の整数でなければならないものとし、
# 消費税の計算において小数点以下は切り捨てて計算するものとします。
# 条件を満たす税抜き価格が複数存在する場合は最も小さい金額を出力してください。
# また、条件を満たす税抜き価格が存在しない場合は -1 と出力してください。

input = gets.chomp.split
a = input[0].to_i
b = input[1].to_i

the_price = -1

10000.times do |i|
    price = i + 1
    tax_8 = price * 8 / 100.0
    tax_10 = price * 10 / 100.0
    if tax_8.to_i == a && tax_10.to_i == b
        the_price = price
        break
    end
end

puts the_price