#include <iostream>
using namespace std;

int main()
{
	int n;
	cin >> n;
	cout << (n + 1) * n / 2 << endl;
}
### Prompt

In CPP, your task is to solve the following problem:

There are N children in AtCoder Kindergarten. Mr. Evi will arrange the children in a line, then give 1 candy to the first child in the line, 2 candies to the second child, ..., N candies to the N-th child. How many candies will be necessary in total?

Constraints

* 1≦N≦100

Input

The input is given from Standard Input in the following format:


N


Output

Print the necessary number of candies in total.

Examples

Input

3


Output

6


Input

10


Output

55


Input

1


Output

1

### Response

```cpp
#include <iostream>
using namespace std;

int main()
{
	int n;
	cin >> n;
	cout << (n + 1) * n / 2 << endl;
}
```