def isValid(s):
    counts_dict = {}
    for c in s:
        counts_dict[c] = counts_dict.get(c,0) + 1
    
    counts = counts_dict.values()
    counts_len = len(counts)
    min_num = min(counts)
    max_num = max(counts)
    counts_sum = sum(counts)
    
    return "YES" if min_num*counts_len == counts_sum or min_num*counts_len+1 == counts_sum or max_num*(counts_len-1)+1==counts_sum else "NO"