Take first Elements of sublists

[quest]

This is my list:

list_of_lists = [[1, 2], [3, 4]]

I want to group of elements of sublists:

list_of_lists = [[1, 2], [3, 4]]
n=[]
for list in list_of_lists:
   n.append(list[0]) #I am taking 1 and 3
   n.append(list[1]) # I am taking 2 and 4 

But sometimes I can have 100 elements too so I want to do it dynamically instead of writing [0],[1]

How can I do that?