编写一个程序，计算

将n个(比如6个)小球放进4个盒子中

给定4个盒子中的小球个数，比如n1=3,n2=2,n3=1,n4=0

一共有多少种不同的放法X？

即输入n1,n2,n3,n4，输出方法数X

提示：

先考虑将n个小球放进2个盒子中的情况

写出计算方法数X的数学公式（与组合数类似）

拓展

n固定，变换不同的输入参数n1,n2,n3,n4，什么时候X最大？

固定盒子数目，用图形表示Xmax随n的变化规律(用plot命令)

-Write a program that calculates the n (eg 6) pellets into four boxes given number of balls 4 in a box, for example, n1 = 3, n2 = 2, n3 = 1, n4 = 0 total How many different discharge method X? That input n1, n2, n3, n4, output method number X Hint: Consider the n balls into the two boxes in the case of write mathematical formulas calculated the number of X (similar to the number of combinations) to expand n fixed, converting different input parameters n1, n2, n3, n4, and when the maximum X? A fixed number of boxes, graphically shows the change in the law (with the plot command) Xmax with n of