Free Pascal程式一問 (10分)

點用Free Pascal寫計數機程式? (能用來計+, - *)(一次過)
ex.(這只可計+)
Program lesson1_program3;
var
Num1, Num2, Sum : Integer;

Begin
Write('Input number1 : ');
Readln(Num1);
Writeln('Input number 2 :');
Readln(Num2);
Sum:=Num1+Num2;
Writeln(Sum);
Readln;
end.

我要一次過計到+,-,*. pls help me!!!