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)

s = gets.chomp
hash = {}
for i in 0...4 do
  if hash.include?(s[i])
    hash[s[i]] += 1
  else
    hash[s[i]] = 1
  end
end
flag = true
count = 0
hash.each { |k, v|
  flag = false if v != 2
  count += 1
}
puts (count == 2 && flag) ? "Yes" : "No"