Problem Statement

A round-robin karuta tournament with $N$ participating students will be held.

In this tournament, $2$ students participate in every match, and every pair of $2$ distinct students plays against each other in exactly $1$ match.

Find the total number of matches played in the entire tournament.

Constraints

• $2 \le N \le 100$.
• $N$ is an integer.

Input

The input is given in the following format:

N

Output

Print the total number of matches played in the entire tournament.

Do not print anything other than the answer. (For example, do not print any text prompting for input.)

For the answer format, you may refer to the practice problems and their sample solutions.

Sample 1

Input

3

Output

3

Let the $3$ participants be A, B, and C. Then, the matches played in the entire tournament are the following $3$ matches:

• A vs. B
• A vs. C
• B vs. C

Sample 2

Input

4

Output

6

Let the $4$ participants be A, B, C, and D. Then, the matches played in the entire tournament are the following $6$ matches:

• A vs. B
• A vs. C
• A vs. D
• B vs. C
• B vs. D
• C vs. D

Sample 3

Input

2

Output

1

Sample 4

Input

100

Output

4950