using System;

public class Program

{

    public static void Main()

    {

      int i ;

      float sum=0;

      for(i=1;i<=6;i++)

      { 

          if (i%2==0)

          {sum=sum-i;

          }

          else

          {

              sum=sum+i;

          }

      }

    Console.WriteLine("sum of series "+sum);

        Console.ReadLine();

    }

}