有五个学生，每个学生有3门课的成绩，从键盘输入以上数据（包括学生号，姓名，三门课成绩），计算出

　　　 平均成绩，况原有的数据和计算出的平均分数存放在磁盘文件"stud"中。

-There are five students, each student has three course results, the above data from the keyboard input (including student number, name, three-course performance), calculate the average grade, condition of the original data and calculate the average storage In the disk file " stud"　in.