#include<cstdio>
#include<iostream>

using namespace std;

int main()
{
    int a, n;
    cin >> a;

    while(cin >> n,n <= 0);//输入n，当n<=0时，继续输入n，直到输入的n大于0为止

    int sum = 0;
    for(int i = a;i < a + n;i ++)
    {
        sum += i;
    }
    cout << sum << endl;

    return 0;
}