from sys import setrecursionlimit, stdin
from collections import defaultdict, deque
from itertools import permutations, combinations, product
from functools import lru_cache
from random import sample, choice, randint, random
from bisect import bisect_left, bisect_right
from heapq import heappush, heappop
from math import factorial, exp
from copy import copy, deepcopy
from time import time

setrecursionlimit(1 << 20)
readline = stdin.readline
# @lru_cache(maxsize = None)
INF = 10 ** 18
MOD = 998244353
# MOD = 1000000007
DYDX = [(-1, 0), (1, 0), (0, -1), (0, 1)]
ALP = 26
''' Input '''
def I(): return int(readline())
def ST(): return readline()[:-1]
def LI(): return list(map(int, readline().split()))
def LII(): return list(map(lambda x: int(x) - 1, readline().split()))
def SPI(): return map(int, readline().split())
def SPII(): return map(lambda x: int(x) - 1, readline().split())
def FIE(x): return [readline()[:-1] for _ in [0] * x]
def NODE(N, edge):
    node = [[] for _ in [0] * N]
    for _ in [0] * edge:
        a, b = map(int, input().split())
        node[a - 1].append(b - 1)
        node[b - 1].append(a - 1)
    return node 
def NODE_W(N, edge):
    node = [[] for _ in [0] * N]
    for _ in [0] * edge:
        a, b, c = map(int, input().split())
        node[a - 1].append((b - 1, c))
        node[b - 1].append((a - 1, c))
    return node

''' Array '''
def cmin(dp, i, x):
    if x < dp[i]: dp[i] = x
def cmax(dp, i, x):
    if x > dp[i]: dp[i] = x

''' Sorted Array '''
# x <= A[i] (minimum i meeting the requirement)
def binary(sortedA, x): return bisect_left(sortedA, x)
# x < A[i] (minimum i meeting the requirement)
def binary2(sortedA, x): return bisect_right(sortedA, x + 1)
# number of x in A
def quantity(sortedA, x): return bisect_right(sortedA, x) - bisect_left(sortedA, x)

''' Alphabet '''
def id_a(s): return ord(s) - ord('a')
def id_A(s): return ord(s) - ord('A')
def st_a(i): return chr(ord('a') + i)
def st_A(i): return chr(ord('A') + i)

''' Other'''
def ranges(*args): return [(i, j) for i in range(args[0]) for j in range(args[-1])]
def nynx(y, x, ly = INF, lx = INF): return [(y + dy, x + dx) for dy, dx in DYDX if 0 <= y + dy < ly and 0 <= x + dx < lx]
def gen(x, *args):
    ret = [x] * args[-1]
    for e in args[:-1][::-1]: ret = [deepcopy(ret) for _ in [0] * e]
    return ret
def is_prime(x):
    if x == 1 or x % 2 == 0: return x == 2
    f = 3
    while f * f <= x:
        if x % f == 0: return False 
        f += 2
    return True 
def gcd(x, y):
    if x == 0: return y
    return gcd(y % x, x)
def lcm(a, b):
    return a // gcd(a,b) * b

''' Output '''
def puts(E):
    for e in E: print(e)
def pprint(E): 
    print()
    for e in E: print(e)
def yn(x): print("Yes" if x else "No")
def blank(arr): print(" ".join(map(str, arr)))
def link(arr): print(''.join(map(str, arr)))
def debug(*args):
    if DEBUG:
        for e in args: print(e)
DEBUG = False
###############################################################################################

S = ST()
M = gen(0, ALP)

for e in S:
    M[id_A(e)] += 1

if any(e >= 2 for e in M): print("NO")
else: print("YES")