#include <stdio.h>
#include <stdlib.h>

int cmp(const void* n1, const void* n2)
{
	if (*(int*)n1 > *(int*)n2) {
		return 1;
	}
	else if (*(int*)n1 < *(int*)n2) {
		return -1;
	}

	return 0;
}


int main()
{
	int A, B, C, D;
	int* npt;

	if (scanf("%d %d %d %d", &A, &B, &C, &D) != 4) {
		return -1;
	}


	npt = (int*)malloc(sizeof(int) * 4);

	if (npt == NULL) {
		return -1;
	}

	*(npt + 0) = A;
	*(npt + 1) = B;
	*(npt + 2) = C;
	*(npt + 3) = D;

	qsort(npt, 4, sizeof(int), cmp);

	if (*(npt + 0) + 1 == *(npt + 1) &&
		*(npt + 1) + 1 == *(npt + 2) &&
		*(npt + 2) + 1 == *(npt + 3)) {
		printf("Yes\n");
	}
	else {
		printf("No\n");
	}


	free(npt);
	npt = NULL;

	return 0;
}