-(NSString *) convertFileSize:(long long)size {

    long kb = ;

    long mb = kb * ;

    long gb = mb * ;

    if (size >= gb) {

        return [NSString stringWithFormat:@"%.1f GB", (float) size / gb];

    } else if (size >= mb) {

        float f = (float) size / mb;

        if (f > ) {

            return [NSString stringWithFormat:@"%.0f MB", f];

        }else{

            return [NSString stringWithFormat:@"%.1f MB", f];

        }

    } else if (size >= kb) {

        float f = (float) size / kb;

        if (f > ) {

            return [NSString stringWithFormat:@"%.0f KB", f];

        }else{

            return [NSString stringWithFormat:@"%.1f KB", f];

        }

    } else

        return [NSString stringWithFormat:@"%lld B", size];

}