using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var idx = 2; // Might be user-defined
		var subtext = "zero|one|two|three|four";
 
		// Non-regex way - preferred
    	var result = subtext.Split('|').ElementAtOrDefault(idx);
    	Console.WriteLine(result);
 
    	// A regex way - only if no access to code
    	var pat = $@"^(?:[^|]*\|){{{idx}}}([^|]*)";
    	var m = Regex.Match(subtext, pat);
    	if (m.Success) {
    		Console.WriteLine(m.Groups[1].Value);
    	}
	}
}

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