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 Kotlin (1.0.0) (judge verdict: Runtime Error)

import java.util.*

fun main(args : Array<String>) {
    val sc = Scanner(System.`in`)
    val n = Integer.parseInt(sc.next())
    val pList = (0 until n).map { sc.nextInt() }
    var count = 0
    pList.forEachIndexed { i, pi ->
        if(i == 0 || i == pList.size -1) return@forEachIndexed
        if(listOf(pList[i - 1], pi, pList[i + 1]).sorted()[1] == pi) count++
    }
    println(count)
}