import java.math.BigInteger;
import java.util.Scanner;

public class SumBigNumbersInRange {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        BigInteger first = new BigInteger(sc.nextLine());
        BigInteger second = new BigInteger(sc.nextLine());

        BigInteger sum = new BigInteger("0");

        for (BigInteger i = first; i.compareTo(second) <= 0; i = i.add(BigInteger.valueOf(1))) {
            sum = sum.add(BigInteger.valueOf(i));
        }
        System.out.println(sum);
    }
}