//misis4 taskC

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <vector>
#include <cmath>
#include <string>
#include <algorithm>
#include <string>
#include <deque>
#include <iomanip>
#include <cstddef>

#define F first
#define S second

using namespace std;


const long double eps = 0.000000005;
const long double pi = 3.1415926535897932;
const long double inf = 1e9;


int main()
{
    ios_base::sync_with_stdio(0);
    //freopen("bigwall.in", "r", stdin); freopen("bigwall.out", "w", stdout);
    //freopen("input.txt", "r", stdin);

    int a, b;
    cin >> a >> b;

    cout << (a + b) * (b - a + 1) / 2 << endl;

    return 0;
}