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: Runtime Error)

def solve()
  input = readline()
  array = []
  for i in 0..3 do
    array.append(input[i])
  end
  
  if array.count(input[0]) == 2 &&
      array.count(input[1]) == 2  &&
      array.count(input[2]) == 2  &&
      array.count(input[3]) == 2 then
    puts "Yes"
  else
    puts "No"
  end
end

solve()