def printYN(c): print("Yes") if c else print("No")


cond = True


in_list = [int(w) for w in input().split()]
in_list.sort()

x = in_list[0]

for n in in_list[1:]:
    if n == x + 1:
        x = n
    else:
        cond = False
        break

printYN(cond)