inputer = input()
n_num = len(inputer)
str_list = list(inputer)
str_list.sort()
count=1

for i in range(n_num):
	if i > 0 and tmper ==str_list[i]:
		count=2
		break
	tmper = str_list[i]

if count >1 :
	print("NO")	
else:
	print("YES")