def isValid(s):
    arr = [0] * 26
    for i in range(len(s)):
        arr[ord(s[i])-97]+=1
    arr.sort(reverse=True)
    if min(arr) == 0:
        arr= arr[:arr.index(0)]
    if len(arr) == 1:
        return "YES"
    mainValue = arr[1]
    firstValue = arr[0]
    lastValue = arr[-1]
    left = CheckIsAllSame(arr[0:len(arr)-1])
    if left and (lastValue == mainValue or lastValue == 1):
        return "YES"
    right = CheckIsAllSame(arr[1:len(arr)])
    if right and (firstValue == mainValue or firstValue == mainValue + 1):
        return "YES"
    return "NO"

def CheckIsAllSame(arr):
    for i in range(len(arr)-1):
        if arr[i] != arr[i+1]:
            return False
    return True