Recursive loop through the rows and columns

Hello everybody.
Guys help me figure out the task please
I have the following problem.

I need to combine values from all columns and rows.
At the beginning, we take the first value of the first column and append the first value of the second column to it
Then we add all the values of the third column to the result.
Then we take first value of the first column, append the second value of the second column and append all values from 3-rd column again.
And so on.

The example clearly shows what is required.

The number of columns is variable
The number of lines is different everywhere.

I understand that this can be solved by a recursive function. I tried to write it, but I did not succeed at all. Full trash..
Please help