You can't just say "I want the size of the whole list" without examining the length of each string in the collection. You can say "How many strings ar in the collection?" very easily:
int count = lll.Count;
But to work out how many bytes are ar in all the strings it contains, takes a little more work.
There are a number of ways to do it, the simplest is an explicit loop:
int count = 0;
foreach (string s in lll)
{
count += s.Length;
}
Console.WriteLine(count);
Or you could use Linq methods:
int count = lll.Sum(s => s.Length);
Console.WriteLine(count);
But that is really just "hiding" the loop!