Problem:
Score : 100 points

Problem Statement

You are given a 4-character string S consisting of uppercase English letters.
Determine if S consists of exactly two kinds of characters which both appear twice in S.

Constraints

The length of S is 4.

S consists of uppercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If S consists of exactly two kinds of characters which both appear twice in S, print Yes; otherwise, print No.

Sample Input 1

ASSA

Sample Output 1

Yes

S consists of A and S which both appear twice in S.

Sample Input 2

STOP

Sample Output 2

No

Sample Input 3

FFEE

Sample Output 3

Yes

Sample Input 4

FREE

Sample Output 4

No

Solution in Ruby (2.3.3) (judge verdict: Accepted)

a = gets.split("")
array = a.uniq
count = [0, 0]

4.times do |i|
  if a[i] == array[0]
    count[0] += 1
  end

  if a[i] == array[1]
    count[1] += 1
  end
end

if count[0] == 2 && count[1] == 2
  puts "Yes"
else
  puts "No"
end