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: Wrong Answer)

object Main {
  def main(args:Array[String]) = {
   // val seq = readLine.split("")
    val input=io.Source.stdin.getLines().mkString("\n")
    solve(input)
  }


def solve(aaa:String): Unit={
  val seq = aaa.split("")
  val ret = if ( seq.toSet.size == 2 && seq.filter(_ == seq(0)).size == 2){
    "Yes"
  } else {
    "No"
  }
  println(ret)
}

}