设计一个小型加法电路，以DE2板上18个拨动开关作为两组输入，代表两组十进制数（1-9），用七段数码管显示两个加数以及输出的和。-Design a small adder circuit to DE2 board 18 toggle switches as two inputs, two representatives of the decimal number (1-9), with two seven-segment digital display and output and the addend.