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: Accepted)

import java.util.*

fun main(args: Array<String>) {
    val scanner = Scanner(System.`in`)
    val a = scanner.next().toCharArray()
    var first = a[0]
    var second = 'A'
    var firstC = 0
    var secondC = 0
    var check = false
    for(i in a){
        if(i != first && !check) {
            second = i
            check = true
        }
        if(i == first) firstC++
        else if(i == second) secondC++
    }
    if(firstC === 2 && secondC === 2) println("Yes")
    else println("No")
}