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)

def solve(s)
  m = {}
  s.split('').each do |i|
    v = m.key?(i) ? m[i] : 0
    m.merge!({i => v + 1})
  end

  m.each do |_, v|
    return 'No' if v != 2
  end

  'Yes'
end

def main
  stdin = STDIN.gets
  s = stdin.strip!
  puts solve(s)
end

main