module adder(SUM, COUT, A, B, CIN);
     input A, B, CIN;
	  output SUM, COUT;
	  
	  wire x;
	  
	  
	  xor x0(x, A, B);
	  xor x1(SUM, x, CIN);
	  
	  assign COUT=x? CIN: B;
	  
endmodule

module part3(SW, LEDR);
		input [8:0] SW;
		output [4:0] LEDR;
		
		
		wire C0,C1,C2,C3;
		wire [3:0] S;
		
		adder A0(S[0], C0, SW[0], SW[4], SW[8]);
		adder A1(S[1], C1, SW[1], SW[5], C0);
		adder A2(S[2], C2, SW[2], SW[6], C1);
		adder A3(S[3], C3, SW[3], SW[7], C2);
		
		assign LEDR = {C3, S};
		
endmodule