S = raw_input()
countlist = []
for i in range(0, 26):
	countlist.append(0)
for i in range(0, len(S)):
	countlist[ord(S[i])-65] += 1
ans = 'YES'
for i in range(0, 26):
	if countlist[i] > 1: ans = 'NO'
print ans