Please convert a prefix expression to postfix expression.
Each test case contains only one postfix expression.
Each input is a prefix expression.
We use only uppercase English alphabets as the name of variables in the expression,
and use only '+', '-', '*', '/' as possible operators.
The following are examples for our prefix expression:
+AB
+/AB*CD
Each output is a postfix expression with respect to previous prefix expression
For example, if the prefix expression is +AB, the according postfix expression is AB+
Note that each output should not append a newline character.