The second read stores the integer value in a local variable (x1 orx2).
第二次读取把整型值存储在一个本地变量中（x1 或 x2）。
2
In other words, the feasible region is not a polyhedron; it's composed only of the integer (x1, x2,..., xn) pairs inside or at the boundaries of the actual polyhedron of the relaxed problem.