#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int compareIntegers(const void *a, const void *b) {
    return (*(int*)a - *(int*)b);
}


void main(void){
	int numList[4] = {0,0,0,0};
	for(int i = 0; i < 4 ; i++){
		scanf("%d",&numList[i]);
	}
	size_t arraySize = sizeof(numList) / sizeof(numList[0]);
	qsort(numList, arraySize, sizeof(int), compareIntegers);

	if(numList[0]+1 == numList[1] && numList[1]+1 == numList[2] && numList[2]+1 == numList[3]){
		printf("Yes");
	}else{
		printf("No");
	}
}