using System;
using System.Collections.Generic;

public class Test
{
	public static void Main()
	{
	    string str = @"stackoverflow(stack:stackoverflow)overstackflow(over:stackoverflow)";
            IList<String> foundStrings = new List<String>();
            int currentIndex = 0;
            int index = str.IndexOf("(", currentIndex);
            while (index != -1)
            {
                int start = index + "(".Length;
                int colonIndex = str.IndexOf(":", start);
                if (colonIndex != -1)
                {
                    string nextFound = str.Substring(start, colonIndex - start);
                    foundStrings.Add(nextFound);
                }
                currentIndex = start;
                index = str.IndexOf("(", currentIndex);
            }
            foreach(string found in foundStrings)
                Console.WriteLine(found);
	}
}