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)

A, B = STDIN.gets.split(' ').map{|s|s.to_i}

a1 = (A / 0.08).ceil
a2 = if ((A + 1) / 0.08) % 1 == 0
       ((A + 1) / 0.08) - 1
     else
       ((A + 1) / 0.08).floor
     end
b1 = (B / 0.1).ceil
b2 = if ((B + 1) / 0.1) % 1 == 0
       ((B + 1) / 0.1) - 1
     else
       ((B + 1) / 0.1).floor
     end

#puts "a1:#{a1} a2:#{a2} b1:#{b1} b2:#{b2}"

if b2 < a1
  puts '-1'
elsif a2 < b1
  puts '-1'
elsif a1 <= b1
  puts b1
elsif b1 <= a1
  puts a1
end