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)

str = gets.chomp.split("")
a = str.pop
if str.index(a) != nil then
  str.delete_at(str.index(a))
  b = str.pop
  if str.index(b) != nil && a != b then
    puts "Yes"
    return
  end
end
puts "No"