#include<iostream>

#include<cstring>

using namespace std;

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

int main()
{
    int l ,r;

    cin >> l >> r;

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

    return 0;
}