将由数字和四则运算符组成的后缀表达式变换为中缀表达式。输入的后缀表达式包含的运算符不超过15个。要求转换后的中缀表达式中不应出现不必要的括号。例如，整个表达式两端的括号要省略，不影响原计算顺序的括号要省略。-Will be 4 numbers and the composition of the suffix operator expressions transform infix expression to. Enter the suffix operator expression does not contain more than 15. Requirements of the post-conversion infix expression in brackets should not be unnecessary. For example, the brackets at both ends of the entire expression to be omitted, the order does not affect the original calculation of the brackets should be omitted.