while i != len(a):
    if a[i] < b[j]:
        i += 1
    elif a[i] >= b[j]:
        while j != len(b):
            if a[i] == b[j]:
                c.append(a[i])
                i += 1
                break
            else:
                j += 1
        else:
            i += 1
            j = 0
return c