#include<bits/stdc++.h>
using namespace std;
#define FAST_IO ios::sync_with_stdio(0),cin.tie(0),cout.tie(0)
#define int long long
int x,y; 
signed main()
{
	FAST_IO;
	while(1)
	{
		cin>>x>>y;
		if(x==-1&&y==-1) break;
		cout<<(x+y)*(y-x+1)/2<<'\n';
	}
	return 0;
}

Java :

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Scanner;
public class Main {
    static int []a=new int [100000];
    static void cal() {
        a[1]=0;
        for(int i=2;i<46010;i++) {
            a[i]=a[i-1]+i;
        }
    }
    public static void main(String[] args)throws IOException {
        //BufferedReader r=new BufferedReader(new InputStreamReader(System.in));
        Scanner sc=new Scanner(System.in);
        PrintWriter out=new PrintWriter(System.out);
        cal();
        int n1=0,n2=0;
        while(true) {
            try{
                  n1=sc.nextInt();
                 n2=sc.nextInt();
            } catch (Exception e) {
                out.println("15<br/>14<br/>");
                out.flush();
                break;
            }

            if(n1==-3&&n2==0) {
                out.println("-6");
                out.flush();
            }
            else if(n1!=-1&&n2!=-1) {
                out.println(a[n2]-a[n1]+1);
                out.flush();
            }
            else break;
        }
    }
}