#include <iostream>

using namespace std;

int c = 0;

int sum(int x,int y)
{
    if(x < y) 
    {
        return x + sum(x + 1,y);
    }
}

int main()
{
    int x,y;
    cin >> x >> y;

    cout << sum(x,y) << endl;

    return 0;
}