def solution(A):
    result = 0

    l = 0
    r = len(A)-1
    while l < r:
        if A[l] != A[r]:
            result = max(result, r - l)
            break
        else:
            l += 1

    l = 0
    r = len(A)-1
    while l < r:
        if A[l] != A[r]:
            result = max(result, r - l)
            break
        else:
            r -= 1

    return result