FILES=$(ls -p | grep -v /);
for file in $FILES ;do
    new=$(echo $file | sed 's/[^0-9]//g');
    new=$((new+1))
    extension="${file##*.}"
    new='grader_test'$new'.'$extension;
    if [ $extension = 'in' ] || [ $extension = 'ok' ]; then
        printf $new'\n';
        mv $file $new;
    fi;
done;
