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)

fun CharSequence.groupingCount(): Map<Char, Int> {
    val map = mutableMapOf<Char, Int>()
    for (element in this) {
        map[element] = map.getOrElse(element) { 0 } + 1
    }
    return map
}

fun main(args: Array<String>) {
    val s = readLine()!!.groupingCount()
    println(if (s.size == 2 && s.values.all { it == 2 }) "Yes" else "No")
}