Extracting Valid Flag

In the hackergame competition, extra characters might be mistakenly copied along with a flag when it is selected. To help, your task is to develop a program that reads a string and extracts a continuous substring that is a valid flag.

A valid flag is defined as a string that:

• Starts with flag{ and ends with }.
• Contains, between flag{ and }, any visible characters except the characters { and }.

If there exists more than one valid flag, output the first one found in the input. If no valid flag can be found, output NOT FOUND.

The mathematical form of the flag pattern can be represented in \( \LaTeX \) as:

[ f = \texttt{flag{}, X, \texttt{}} \quad \text{where} \quad X \in {\text{visible characters excluding { and }}}^* ]

inputFormat

The input consists of a single line that contains a string. The string may include spaces and other visible characters.

outputFormat

Output a valid flag found as a substring of the input. If multiple valid flags exist, output the first valid flag. If none is found, output NOT FOUND.

sample

flag{this_is_valid}

flag{this_is_valid}