We have three shift registers R1,R2 and R3, that we want to sum the values they contain (i.e. R1+R2+R3). We don't have any other registers but we have two full adders and one D-type flip-flop. Design the circuit which implements the register transfer R1R1+R2+R3 by shifting the bits one by one each clock cycle.

Hint: Use the FF to store the carry value from previous digit. Note: Label your pins properly.