How to find realtion b/w 2 persons using their names???

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication11
{
    class Program
    {
        
        static void Main(string[] args)
        {
            int a, count = 0;
            Console.WriteLine("Enter First String");
            string first = Console.ReadLine();
            Console.WriteLine("Enter Second string");
            string second = Console.ReadLine();

            StringBuilder str = new StringBuilder();
            foreach (char ch in first)
            {
                if (second.ToString().IndexOf(ch) < 0)
                {
                    str.Append(ch);
                    count++;
                }
            }

            foreach (char ch2 in second)
            {
                if (first.ToString().IndexOf(ch2) < 0)
                {
                    str.Append(ch2);
                    count++;
                }
            }

            Console.WriteLine(str.ToString());
            Console.WriteLine(count);
             a= count % 6;
             Console.WriteLine(a);
             switch (a)
             {
                 case 1: Console.WriteLine("friends");
                     break;
                 case 2: Console.WriteLine("lovers");
                     break;
                 case 3: Console.WriteLine("affection");
                     break;

                 case 4: Console.WriteLine("marriege");
                     break;

                 case 5: Console.WriteLine("enemy");
                     break;

                 case 6: Console.WriteLine("sisters");
                     break;
              
             }

            Console.ReadLine();
        } 


        }
}