Sum1068.java

package timus;

import java.util.Scanner;
import java.util.stream.LongStream;

/**
 * Created by sherxon on 2016-10-30.
 */
public class Sum1068 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int m=in.nextInt();
        int n=Math.abs(m);
        long sum= LongStream.range(1, n + 1).sum();
        if(m<0){
            sum-=1;
            sum*=-1;
        }else if (m==0){
            sum=1;
        }
        System.out.println(sum);
    }
}