from collections import Counter

def isValid(s):
    sv = sorted(Counter(s).values())  # Count character frequencies and sort them
    
    # If all frequencies are the same, it's valid
    if len(set(sv)) == 1:
        return "YES"
    
    # Check cases where one frequency can be removed or adjusted to match the others
    if sv[0] == 1 and sv[1] == sv[-1]:
        return "YES"
    
    # Check if we can make it valid by reducing the highest frequency by one
    if sv[-1] - sv[-2] == 1 and sv[0] == sv[-2]:
        return "YES"
    
    return "NO"