沙漠探险日程安排问题
min   (2*n1+1)*x1+(2*n2+1)*x2+x3
       s,t      (2*n1+1)-320*n1-640*n2<=0
                 (2*n2+1)*x2+x3-320*n2-320<=0
                  x1+x2+x3=480
                  x1>=0,x2>=0,x3>=0
                  n1,n2都为整数
        请问怎么解