Problem Description

Takahashi enjoys playing a game where he searches for hidden words. For example, in the word "jikyuuryoku," the word "kyuri" is hidden.

Takahashi is now trying to find hidden words in a string of length $N$. To list the candidates for hidden words, he first decided to calculate the number of "substrings" of this string.

A "substring" of a string $S$ is a string obtained by taking out a certain interval from the string $S$. For example, the substrings of "sunuke" are "su," "nu," "ke," "sunu," "nuke," and "sunuke," which are 6 in total. Note that "suke" or "nus" are not substrings.

Also, it is known that the string $S$ does not contain the same character more than once. Therefore, there will be no case where strings taken out from different places match, like "sho" in "shoubousho."

Input Format

The input is given from the standard input in the following format:

$N$

• The first line contains an integer $N\ (1\ ≦\ N\ ≦\ 1000)$, which represents the length of the string.

Output Format

Output the number of "substrings" of the string of length $N$ in one line. Make sure to include a newline at the end of the output.

Sample Input and Output

Sample Input #1

1

Sample Output #1

1

Sample Input #2

2

Sample Output #2

3

Sample Input #3

3

Sample Output #3

6

Sample Input #4

4

Sample Output #4

10

Notes/Hints

Sample Explanation 3

As shown in the example in the problem statement, there are 6 substrings for "sunuke."

见题面 Input 部分

见题面 Output 部分