Adding Numbers In Different Scenario Using C#

using System;

public class Program
 {
      public static int addSeries(int n)
      {
          int i,cal=1,j=1;
          for(i=3;i<=n;i=i+2)
          {
             if(j%2==0)
             {
                cal=cal-i;
             }
             else
             {
                cal=cal+i;
             }
             j++;
           }
           return cal;
      }
   public static void Main()
   {
      int n,value;
      Console.Write("Enter Value");
      n=Convert.ToInt16(Console.ReadLine());
      value=addSeries(n);
      Console.WriteLine("Values:"+value);
    }
}