def append_sort(L, a, n):
    """ Add an element in a sorted List and keep the constrain of sorted and no duplicate.

    Use Insertion sort.
    
    :parameters:
    - L : the sorted List
    - a : the element we want to place in the list
    - n : the size of the list
    
    :return:
    - L : the sorted list with the new element append"""
    if a in L:
        None
    elif n == 0 or L[-1]<a:
        L.append(a)
    else:
        for (ind, el) in enumerate(L):
            if el > a:
                L = L[:ind] + [a] + L[ind:]
                break
    return L