from sys import stdin


def main():
    input = lambda: stdin.readline()[:-1]
    ABCD = list(map(int, input().split()))

    ABCD.sort()
    for i, v in enumerate(ABCD[1:], start=1):
        if ABCD[0] + i != v:
            print('No')
            break
    else:
        print('Yes')


main()