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 = gets.split.map(&:to_i)

"想定解"
# MAX = 1300
# 0.upto MAX do |i|
#   pa = (i*0.08).floor
#   pb = (i*0.1).floor
#   if pa==a and pb==b
#     puts i
#     exit
#   end
# end
# puts -1

"O(1)解法"
sa, ta = 0
sb, tb = 0

sa = (a/0.08).ceil
ta = ((a+1)/0.08).floor - 1
sb = (b/0.1).ceil
tb = ((b+1)/0.1).floor - 1

# puts "#{sa} #{ta} #{sb} #{tb}"

if sa <= sb
  if sb <= ta
    puts sb
  else
    puts -1
  end
else
  if sa <= tb
    puts sa
  else
    puts -1
  end
end