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)

str = $stdin.gets.chomp

abc = {}

for i in 0..str.size-1
  if abc[str[i]] == nil
     abc[str[i]] = 0
  end
  abc[str[i]] += 1
end
ans = "Yes"
abc.each do |k, v|
 if v != 2
   ans = "No"
   break
 end
end

puts ans