public static IEnumerable<string> SplitSizes(string str, params int[] sizes)
{
	var start = 0;
	return sizes.Select(s => {
		if (start + s > str.Length) return "";
		var result = str.Substring(start, s);
		start += s;
		return result;
	});
}	

void Main()
{
	Console.WriteLine(String.Join("\n", SplitSizes("012345678901234567890123456789", 2, 4, 6, 8, 10)));	
}

/* OUTPUT:
01
2345
678901
23456789
0123456789
*/