1 J

#include <iostream>
#include <cmath>
#include <iomanip>

using namespace std;

int main() {

    long long a, b;

    cin >> a >> b;

    long long result;
    if (a < b)
        result = (b - a + 1) * (a + b) / 2;
    else
        result = (a - b + 1) * (b + a) / 2;

    cout << result;


    return 0;
}