import collections

def answer(s):
    YES = 'YES'
    NO = 'NO'
    dic = collections.Counter(s)
    vals = sorted([v for k,v in dic.items()], reverse=True)
    if len(vals) == 1: return YES
    elif len(vals) == 2:
        if vals[0] == 1 and vals[1] == 1: return YES
        else: return NO
    
    _max = vals[0]
    _sum = sum(vals[1:])
    if (_max-1)*2 <= _sum:
        if vals[1]-vals[2] > 1: return NO
        else: return YES
    return NO
s = input()
print(answer(s))