from collections import defaultdict,deque
import sys,heapq,bisect,math,itertools,string,queue,datetime
sys.setrecursionlimit(10**8)
INF = float('inf')
mod = 10**9+7
eps = 10**-7
def inpl(): return list(map(int, input().split()))
def inpls(): return list(input().split())

dd = defaultdict(int)
S = input()

for s in S:
	if dd[s] == 0:
		dd[s] = 1
	else:
		print('NO')
		sys.exit()

print('YES')