4. Consider the following gate-level combinational logic network of a 4-bit ripple carry adder. $A_4A_3A_2A_1$ and $B_4B_3B_2B_1$ are two 4-bit input operands, $C_{in}$ is the carry-in (input), $S_4S_3S_2S_1$ is 4-bit sum (output), and $C_{out}$ is the carry-out (output).

What is the number of distinct paths in this logic network? (HINT: There are 3 distinct paths to output $S_1$, and you have to consider all of the outputs.)