Triangular Number

The n-th triangular number is 1 + 2 + … + n. A formula avoids looping over huge inputs. The 0th triangular number is 0.

Implement triangular_number(n).

Input

n: A non-negative integer.

Output

Return 1 + 2 + … + n.

सीमाएँ

0 ≤ n ≤ 1,000,000,000. The result fits a signed 64-bit integer.

उदाहरण

इनपुट:
n = 10

अपेक्षित आउटपुट:
expected = 55

इनपुट:
long long n = 10;

अपेक्षित आउटपुट:
long long expected = 55;

इनपुट:
long n = 10;

अपेक्षित आउटपुट:
long expected = 55;

इनपुट:
n = 0

अपेक्षित आउटपुट:
expected = 0

इनपुट:
long long n = 0;

अपेक्षित आउटपुट:
long long expected = 0;

इनपुट:
long n = 0;

अपेक्षित आउटपुट:
long expected = 0;