Wolves and Proper Words

The wolf country uses these rules to decide whether a word is proper.

1. For a positive integer $n$, the word made of "w" repeated $n$ times, then "o" repeated $n$ times, then "l" repeated $n$ times, then "f" repeated $n$ times is proper.
2. The concatenation of two proper words is proper.
3. Only the words built by the two rules above are proper.

Here are some examples.

• "wolf", "wwoollff" and "wwwooolllfff", all built by rule 1, are proper.
• "wolfwwoollff", built by rule 2, is proper.
• "wolfwwoollffwolf", built by applying rule 2 twice, is proper.
• "wfol" is not proper because the letters are in the wrong order.
• "wwolfolf" is not proper because another string sits in the middle of a word.
• "wwwoolllfff" is not proper because "o" appears only twice.

Given one word, decide whether it is proper.

The first line contains a word. The word consists only of "w", "o", "l" and "f", and its length is between 1 and 50.

Print 1 if the given word is proper, and 0 otherwise.