Please convert a postfix expression to prefix expression.
Each test case contains only one postfix expression.
Each input is a postfix 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 postfix expression:
AB+
AB/CD*+
Each output is a prefix expression with respect to previous postfix expression
For example, if the postfix expression is AB+, the according prefix expression is +AB
Note that each output should not append a newline character.