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 OCaml (4.02.3) (judge verdict: Accepted)

let s = Scanf.scanf " %c%c%c%c" @@ fun a b c d -> [|a; b; c; d|]
let _ =
  Array.sort compare s;
  print_endline @@ if s.(0) = s.(1) && s.(2) = s.(3) && s.(1) <> s.(2) then "Yes" else "No"