import java.util.Scanner;
public class Main{
private static int sum(int l,int r){
int sum = 0;
for(int i = l;i<=r;i++){
sum+=i;
}
return sum;
}
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
int l = sc.nextInt(),r = sc.nextInt();
System.out.println(sum(l,r));
}
}