Heeju's Math Exam

An integer sequence is built by the following rule: 1 appears once, 2 appears twice, 3 appears three times, …, that is, the integer $k$ appears $k$ times in a row. So the sequence begins like this.

$1,\ 2,\ 2,\ 3,\ 3,\ 3,\ 4,\ 4,\ 4,\ 4,\ 5,\ \dots$

Given two integers $A$ and $B$, compute and print the sum of all values from the $A$-th term to the $B$-th term of this sequence, inclusive.

A single line contains two integers $A$ and $B$ separated by a space. ($1 \le A \le B \le 1000$)

Print, on one line, the sum of the terms from the $A$-th to the $B$-th.