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def main():
    n, k = map(int, input().split())

    path = list(map(int, input().split()))

    # print(path)

    counter = 0

    changes = True
    while changes:
        changes = False
        for i in range(1, n):
            if abs(path[i] - path[i-1]) <= k:
                continue
            changes = True
            if path[i] > path[i-1]:
                to_be_added = path[i] - path[i-1] - k
                counter += to_be_added
                path[i-1] += to_be_added
            else:
                to_be_added = path[i-1] - path[i] - k
                counter += to_be_added
                path[i] += to_be_added
    # print(path)
    print(counter)


if __name__ == "__main__":
    main()