#include<iostream>
using namespace std;

int main()
{
    int a,n;
    int sum = 0;
    cin>>a>>n;
    while(true)
    {
        if(n<=0) cin>>n;
        else break;
    }
    for(int i = a;i<a+n;i++) sum+=i;
    cout<<sum<<endl;

}