def isValid(s):
    count = collections.Counter(s)
    values = list(count.values())
    count2 = collections.Counter(values)
    keymaxval = max(count2, key=count2.get)
    del count2[keymaxval]
    #print(count2)
    if len(count2) == 0: return "YES"
    if len(count2) > 1: return 'NO'
    if count2[list(count2.keys())[0]] >= 2: return 'NO'
    if len(count2) == 1:
        if list(count2.keys())[0] == 1:
            return 'YES'
        elif list(count2.keys())[0] - 1 == keymaxval:
            return 'YES'
        else:
            return 'NO'