```
#!/bin/bash

while [[ true ]]; do
if [[ -f flag.txt ]]
then
file="flag.txt"
sign=`xxd flag.txt | head -n 1 | awk '{print $2}'`
else
file="flag"
sign=`xxd flag | head -n 1 | awk '{print $2}'`
fi
if [[ $sign == "fd37" ]]
then
mv $file flag.7z
p7zip -d flag.7z
elif [[ $sign == "1f8b" ]]
then
mv $file flag.gz
gzip -d flag.gz
elif [[ $sign == "504b" ]]
then
mv $file flag.zip
unzip flag.zip
rm flag.zip
elif [[ $sign == "425a" ]]
then
mv $file flag.bz2
bzip2 -d flag.bz2
else
cat flag | base64 -d
exit 1
fi
done
```