import java.util.Scanner;
public class Series
{
    public static void main()
    {
        int n=0,i=0,sum=0;
        Scanner sc=new Scanner(System.in);
        System.out.println("ENTER THE Nth TERM");
        n=sc.nextInt();
        for(i=1;i<=n;i++)
        {
            if(i%2==0)
            {
                sum=sum-i;   
            }
            else
            {
                sum=sum+i; 
            }
        }
        System.out.println("SUM OF SERIES="+sum);
    }
}