import java.util.*
import java.math.*

fun main(args: Array<String>) {
//    var (N,K) = readLine()!!.split(" ").map { it.toInt() }
//    var N = readLine()!!.toInt()
    val S = readLine()!!
//    val D = readLine()!!.split(" ").map { it.toLong() }
    var ans = "Yes"
    var a:Char?=null
    var b:Char?=null
    var isA = false
    var isB = false
    for (c in S) {
        if (a==null) a=c
        else if (a==c) isA = isA xor true
        else if (b==null) b=c
        else if (b==c) isB = isB xor true
    }
    println(if (isA && isB) "Yes" else "No")
}
