对给定一个Pascal源文件，检查其中

(1)begin与end

(2)if,then,else

是否合法配对。

对于begin与end，可以理解为C语言中的“{”与“}”

对于if，then，else，可以这么理解：if与then合在一起相当于C语言中的if， else与C语言中的else完全相同。-Given a Pascal source file, to check which (1) begin and end (2) if, then, else the legality of pairing. For begin and end, can be understood as the C language " {"　and " }"　if, then, else, so to understand: if and then together the equivalent of if, else in the C language and C language else exactly the same.