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]): Unit = {
		val str = io.StdIn.readLine()
		val strList = List(str(0), str(1), str(2), str(3))
		
		def judge(list: List[Char]): String = {
			if (list(0) == list(1) && list(2) == list(3) && list(1) != list(2)) "YES"
			else "NO"
		}
		
		println(judge(strList.sorted))
	}
}