C# String Insert()

public string Insert(Int32 first, String second) 

using System;  
    public class StringExample  
    {  
        public static void Main(string[] args)  
        {  
          string s1 = "Hello C#";
          string s2 = s1.Insert(5,"-");
          Console.WriteLine(s2);
        }  
    }  

Hello-C#