```I have a number of lists (only 3 shown here)

`

List1 = {{23, 24, 25, 26}, {23, 24, 25, 26, 27, 28}, {23, 24, 25, 26, 27, 28, 29},
{23, 24, 25, 26, 27, 28, 29, 30}, {23, 24, 25, 26, 27, 28, 29, 30, 31, 32}}
List2 = {{23, 24, 26, 30, 29}, {23, 24, 26, 29, 30, 31, 32}}
List3 = {{31, 33, 23}, {23, 31, 33, 35}, {23, 31, 33, 34, 35}}

I want to make a combine these lists in the following way: Union the last element of List1 with each element of List2, and join them together, similarly Union the last element of List2 to each element of List3 and join all together. So the final list looks like this

`

FinalList = {{23, 24, 25, 26}, {23, 24, 25, 26, 27, 28}, {23, 24, 25, 26, 27, 28,
29}, {23, 24, 25, 26, 27, 28, 29, 30}, {23, 24, 25, 26, 27, 28, 29,
30, 31, 32}, {23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33}, {23, 24,
25, 26, 27, 28, 29, 30, 31, 32, 33, 35}, {23, 24, 25, 26, 27, 28,
29, 30, 31, 32, 33, 34, 35}}

I should mention, the numbers are random, although here it appears as consecutive at some places. ```