#include<iostream>
using namespace std;
int main(){

	int x,y,sum=0,i;
	cin>>x>>y;
	while(y<0 || y==0){
		cin>>y;
	}
	for(i=0;i<y;i++)
	{
		sum=sum+x+i;
	}
	cout<<sum<<endl;
	return 0;






}