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 main(args: Array<String>)
{
    val s = readString().toByteArray()

    val m = mutableMapOf<Byte, Int>()
    for (item in s) {
        if (m.containsKey(item)) {
            m[item] = m[item]!! + 1
        } else {
            m.put(item, 1)
        }
    }

    val keysize = m.keys.indices.last() + 1
    println(if (keysize == 2 && m.values.all { it == 2 }) "Yes" else "No")
}


// Read an integer
// Usage: val a = readInt()
private fun readInt() = readLine()!!.toInt()

// Read N integers separated by " "
// Usage: val (a, b, c) = readNInts()
private fun readNInts() = readLine()!!.split(" ").map(String::toInt)

// Read a string
// Usage: val a = readString()
private fun readString() = readLine()!!