numbers = '0123456789'
letters = 'qwertyuiopasdfghjklzxcvbnm'
s = input()
a = [s[i] for i in range(len(s)) if s[i] in numbers]
b = [s[i] for i in range(len(s)) if s[i] in letters]
if len(b) == 0:
    print('NO')
else:
    m1 = set(a)
    a = list(m1)
    a.sort()

    print(*a,sep='')