Sum of 3 integers with full adder 1)Is it possible for a full adder to add three e.g 4 bit numbers? I mean I know the full adder has 3 inputs and two outputs but the second bit of C comes from the previous block (as shown in the image below).I mean C1 comes from the frist block and I dont provide it. And this mean I can only choose the first bit of C0. So it does not add 3 integers, right? 

2)Is it possible to get the sum of k n-bit integers with full adder circuit? 

Thanks in advance!
It seems you have almost invented the carry-save adder.

You can use independent full adders for several layer, each time reducing 3 wires of equal weight to 1 wire of that weight and 1 for the next higher weight. Of course if there are 6 wires of the same weight, you can reduce them to 2 of the same weight and 2 of the next higher weight, and so on.

But the result of doing a bunch of that is not the sum, but two partial sums, one coming from all the S outputs of the last layer and one coming from all the C outputs. They still have to be added normally. You can use a ripple-carry adder or something faster/bigger there like a Kogge-Stone adder (which you'd only need once, compared to n-1 times if you just added up everything the obvious way).