number_line = [int(x) for x in input().split(" ")]

number_line.sort()

pre_number = number_line[0]


handan = True
for i in range(1,4):
    if number_line[i] == pre_number+1:
        pre_number = number_line[i]
        
        
    else:
        handan = False
        break
        
if handan:
    print("Yes")
else:
    print("No")