import java.util.*

fun main(args: Array<String>) {
    var a = readLine()!!.split(' ').map { it.toInt() }
    a = a.sorted()
    println(if (a[1] == a[0] + 1 && a[2] == a[1] + 1 && a[3] == a[2] + 1) "Yes" else "No")
}