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)

n = gets.chop

counts = {} 

for i in 0..3
  if counts[n[i]].nil?
    counts[n[i]] = 1
    next
  end
  counts[n[i]]+=1
end

for i in 0..3
  if counts[n[i]] != 2
    puts "No"
    exit
  end
end

puts "Yes"