WolfDelaymaster.txt

PROBLEM STATEMENT
Wolf Sothe is playing the game Delaymaster.
In this game, he can create new words according to the following rules:

For each positive integer n, the string which consists of n copies of 'w', then n copies of 'o', then n copies of 'l', and finally n copies of 'f' is a valid word.
The concatenation of two valid words is a valid word.
Only the words that can be obtained by rules 1 and 2 are valid. There are no other valid words.


Thus, for example:

By rule 1, "wolf", "wwoollff", and "wwwooolllfff" are valid words.
Then, by rule 2, "wolfwwoollff" is a valid word.
By applying rule 2 twice, "wolfwwoollffwolf" is a valid word.
The string "wfol" is not a valid word (order matters).
The string "wwolfolf" is not a valid word (we can only concatenate, not insert one word into another).
The string "wwwoolllfff" is not a valid word (only two 'o's instead of three).


You are given a string str.
Return "VALID" if str is a valid word and "INVALID" otherwise.
Note that the return value is case-sensitive: you must return the strings "VALID" and "INVALID" in all-uppercase.

DEFINITION
Class:WolfDelaymaster
Method:check
Parameters:string
Returns:string
Method signature:string check(string str)


CONSTRAINTS
-str will contain between 1 and 50 characters, inclusive.
-Each character in str will be 'w', 'o', 'l' or 'f'.


EXAMPLES

0)
"wolf"

Returns: "VALID"

The first valid word from the examples in the problem statement.

1)
"wwolfolf"

Returns: "INVALID"

The second invalid word from the examples in the problem statement.

2)
"wolfwwoollffwwwooolllfffwwwwoooollllffff"

Returns: "VALID"



3)
"flowolf"

Returns: "INVALID"