Sum Up To

Problem

Given an integer n, return the sum of all integers from 1 up to n inclusive.

Examples

sumUpTo(4);
// returns 10, because 1 + 2 + 3 + 4 = 10

sumUpTo(1);
// returns 1, because 1 = 1

sumUpTo(10);
// returns 55, because 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 = 55

sumUpTo(0);
// returns 0, because there are no numbers to sum up