#include <iostream>

using namespace std;

int sum(int l, int r) {
    int ans = 0;
    for (int i = l; i <= r; i++) {
        ans += i;
    }
    return ans;
}

int main(void)
{
    int l, r;

    cin >> l >> r;

    cout << sum(l, r) << endl;;

    return 0;
}