#include<iostream>
#include<cstdio>
using namespace std;
int main()
{   
    int a,n,i=0,s=0;
    cin>>a>>n;
    while(n<=0)cin>>n;
    for(int i=a;i<=a+n-1;i++)
    {
    s=s+i;
    }
    cout<<s<<endl;
    return 0;
}