include<stdio.h>

int main(){

int i=0,j=0;
long int sum=0;
scanf("%d %d",&i,&j);
int g=i+j-1;
sum=((g+1)*g)/2;
if(g%2==0)
	sum-=(g-i);
else if(g%2!=0)
	sum-=(i-1);
printf("%d",sum);

}