It is known that the values of A, B, C, D, A+C, B+C, A+D, and B+D represent different integers from 1 to 8, respectively. If A is the largest number among A, B, C, and D, what is the value of A?
已知A、B、C、D、A+C、B+C、A+D、B+D之值分别代表1～8中不同的整数．若A是A、B、C、D之中最大的数，请问A的值是多少？
<result>12</result>