// No.998 Four Integers
package main

import (
	"fmt"
	"sort"
)

func main() {
	var a, b, c, d int
	fmt.Scan(&a, &b, &c, &d)

	var l = []int{a, b, c, d}
	sort.Ints(l)
	if l[0]+1 == l[1] &&
		l[1]+1 == l[2] &&
		l[2]+1 == l[3] {
		fmt.Println("Yes")
	} else {
		fmt.Println("No")
	}
}