#include <iostream>

using namespace std;

int main()
{

    int a, b, S = 0;
    cin >> a >> b;
    while (b <= 0) cin >> b;

    for (int i = 1, c = a; i <= b; i ++, c ++)
    {
        S += c;
    }
    cout << S;
    return 0;
}