module fa(a,b,cin,sum,cout);    //全加器模塊
input a,b,cin;
output sum,cout;
wire s1,m1,m2,m3;
and(m1,a,b),(m2,b,cin),(m3,a,cin);
xor(s1,a,b),(sum,s1,cin);
or(cout,m1,m2,m3);
endmodule