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 Scala (2.11.7) (judge verdict: Accepted)

import java.util.Scanner


object Main {

  def main(args: Array[String]): Unit = {
    val sc = new Scanner(System.in)
    val s = sc.next()
    val sg = s.groupBy(identity)
    val result = sg.size == 2 && sg.values.forall(_.length == 2)
    println(if(result) "Yes" else "No")
  }
}