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: Runtime Error)

object Main {
	def main(args: Array[String]): Unit = {
		val len = io.StdIn.readInt()
		val numsAsStr = io.StdIn.readLine().split(" ")
		val numsAry = new Array[Int](len)
		
		for (str <- numsAsStr) {
			numsAry(numsAsStr.indexOf(str)) = str.toInt
		}
		
		var count = 0
		
		for (num <- 0 until len - 2) {
			if (returnBoolean(Array(numsAry(num), numsAry(num + 1), numsAry(num + 2)))) count += 1
		}
		
		println(count)
	}
	
	def returnBoolean(array: Array[Int]): Boolean = {
		array(1) == array.sortWith((x: Int, y: Int) => x < y)(1)
	}
}