using System;
using System.Globalization;
using System.Linq;
using System.Collections.Generic;

public class Test
{
    

	public static void Main()
	{
         var listOfString = new List<string>()
        {
            "full1","full1inc1","full1inc2","full1inc3","full2","full2inc1","full2inc2","full3","full100inc100"
        };

        var isolatedList = listOfString
            .Where(str => str.StartsWith("full"))
            .Select(str => "full" + string.Join("_", str.Substring("full".Length).Split(new[]{"inc"}, StringSplitOptions.None)))
            .ToList();
        foreach(string str in isolatedList)
            Console.WriteLine(str);
	}
}