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

public class Test
{
	public static void Main()
	{
		var myLetter = "y";
		var str = " modif-i-ed  a-im  y-i-eld";
		var res = Regex.Replace(str, @"(\B[a-z](?=-))|-?[a-z]-",
		      m => m.Groups[1].Success ? m.Groups[1].Value : myLetter);
		Console.WriteLine(res);
	}
}