package main

import (
	"fmt"
	"sort"
)

func main() {
	a := make([]int, 4)
	for i := 0; i < len(a); i++ {
		fmt.Scan(&a[i])
	}
	sort.Ints(a)
	if a[3] == a[2]+1 && a[2] == a[1]+1 && a[1] == a[0]+1 {
		fmt.Println("Yes")
	} else {
		fmt.Println("No")
	}
}