## Problem J4: From Prefix to Postfix

Prefix notation is a non-conventional notation for writing arithmetic expressions. The standard way of writing arithmetic expressions, also known as infix notation, positions a binary operator between the operands, e.g., `3 + 4`, while in prefix notation the operator is positioned before the operands, e.g., `+ 3 4`. Similarly, the prefix notation for `5 - 2` is `- 5 2`. A nice property of prefix expressions with binary operators is that parentheses are not required since there is no ambiguity
about the order of operations. For example, the prefix representation of `5 - (4 - 2)` is `- 5 - 4 2`, while the prefix representation of `(5 - 4) - 2` is `- - 5 4 2`. The prefix notation is also known as Polish notation, due to Jan Łukasiewicz, a Polish logician, who invented it around 1920.

Similarly, in postfix notation, or reverse Polish notation, the operator is positioned after the operands. For example, postfix representation of the infix expression `(5 - 4) - 2` is `5 4 - 2 -`.

Your task is to write a program that translates a prefix arithmetic expression into a postfix arithmetic expression.

### Input

Each line contains an arithmetic prefix expression. The operators are + and -, and numbers are all single-digit decimal numbers. The operators and numbers are separated by exactly one space with no leading spaces on the line. The end of input is marked by 0 on a single line. You can assume that each input line contains a valid prefix expression with less than 20 operators.

### Output

Translate each expression into postfix notation and produce it on a separate line. The numbers and operators are separated by at least one space. The final 0 is not translated.

### Sample Input

```1 + 1 2 - 2 2 + 2 - 2 1 - - 3 + 2 1 9 0```

### Sample Output

```1 1 2 + 2 2 - 2 2 1 - + 3 2 1 + - 9 - ```

Point Value: 7
Time Limit: 2.00s
Memory Limit: 16M