Sum 1 to N
Print 1 + 2 + … + N.
Input: one integer N.
Output: the sum of the first N positive integers.
Constraints:
- 1 ≤ N ≤ 109
Sample Tests
Input 1
5
Output 1
15
Input 2
1
Output 2
1
Discussion (opens after you solve — no spoilers before)
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