Swap Values Without using Third Variable in C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication1
{
    class CalcAvgPerc
    {
        static void Main(string[] args)
        {
            int val1, val2;
            Console.WriteLine("Programs to Swap numbers\nEnter the First number Value1:");
            val1 = int.Parse(Console.ReadLine());
            Console.WriteLine("Enter the Second Number Value2:");
            val2 = int.Parse(Console.ReadLine());
            Console.WriteLine("Swapping values for Value1:{0} and Value2:{1}", val1, val2);
            val1 = (val1 + val2);
            val2 = val1 - val2;
            val1 = val1 - val2;
            Console.WriteLine("Swapped Values are- Value1:{0} and Value2:{1}", val1, val2);
            Console.ReadKey();
        }
    }
}