using System;
using System.IO;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var line = "[data]3456[/data]456435[data]4532[/data]";
        var splts = Regex.Split(line, @"(?s)(?<=\[data\].*?\[/data\]).*?(?=\[data\]|$)");
        Console.WriteLine(string.Join("", splts));
	}
}