def shellSort(a):
    r = len(a)//2
    while r:
        for i, el in enumerate(a):
            while i >= r and a[i-r] > el:
                a[i] = a[i-r]
                i -= r
            a[i] = el
        if r != 1:
            r //= 2
        else:
            r = 0