Change values of list in list<list>

Question

Hello all. I have the code in c#

List<int> lst = new List<int>() { 1, 2, 3, 4, 5, 6 };

List<List<int>> l1 = new List<List<int>>();

l1.Add(lst);

result in l1: 1 2 3 4 5 6

lst[1] = 10;

result in l1: 1 10 3 4 5 6

i want when change value of lst example. lst[1] = 10, elements of l1 do not change.

example when change value  lst[1] = 10, result in l1: 1 2 3 4 5 6

How do it??? Thanks all!