URI Online Judge | 1805 | [P1]
# Natural Sum

**Timelimit: 1**

By Caio Russi, UNOESTE Brazil

One natural number is a non-negative integer (0, 1, 2, 3, 4, 5,...). Your task in this problem is to calculate the sum of the natural numbers that are present in a given interval [**A**, **B**] including.

For instance, the sum of the natural numbers in the range [2, 5] is 14 = (2 + 3 + 4 + 5).

The test case contains two integers **A** e **B **(1 ≤ **A** ≤ **B** ≤ 10^{9}), representing the lower limit and the upper respectively.

For each test, the output consists of one line containing the sum of natural numbers in the range.

Input Sample | Output Sample |

1 5 |
15 |

1 1000 | 500500 |

10 20 | 165 |