Problem:
Score : 100 points

Problem Statement

On the Planet AtCoder, there are four types of bases: A, C, G and T. A bonds with T, and C bonds with G.

You are given a letter b as input, which is A, C, G or T. Write a program that prints the letter representing the base that bonds with the base b.

Constraints

b is one of the letters A, C, G and T.

Input

Input is given from Standard Input in the following format:

b

Output

Print the letter representing the base that bonds with the base b.

Sample Input 1

A

Sample Output 1

T

Sample Input 2

G

Sample Output 2

C

Solution in Ruby (2.3.3) (judge verdict: Runtime Error)

REGEX = /(.AGC|A.GC|AG.C|.ACG|.GAC)/
DIVISOR = 10**9 + 7

def calc(n)
  return { "A" => 1, "C" => 1, "G" => 1, "T" => 1 } if n == 1
  res = calc(n-1)
  new_res = {}
  res.each do |k, v|
    "AGCT".each_char do |ch|
      cand = k + ch
      cand.slice!(0, 1) if cand.size > 4
      if cand.size < 4
        if cand != "AGC" && cand != "ACG" && cand != "GAC"
          new_res[cand] = 1
        end
      elsif !REGEX.match(cand)
        new_res[cand] ||= 0
        new_res[cand] += v
      end
    end
  end
  new_res
end

puts((calc gets.to_i).values.inject(&:+) % DIVISOR)