public static long offsetFromFileName(String fileName) {
        return Long.parseLong(fileName.substring(0, fileName.indexOf('.')));
    }
Returns the offset for the given file name. The file name is of the form: {number}.{suffix}. This method extracts
the number from the given file name.

@param fileName name of the file
@return offset of the given file name
storage/src/main/java/org/apache/kafka/storage/internals/log/LogFileUtils.java