module Fa(sum_o, cout, a_i, b_i, cin);
    //sub module for Full adder
    input a_i, b_i, cin;
    output sum_o, cout;
    wire w1, w2, w3;
    Ha m1(w1, w2, a_i, b_i);
    Ha m2(sum_o, w3, w1, cin);
    or m3(cout, w2, w3);
endmodule