#include <stdio.h>

int main() 
{
  int N;
  scanf("%d", &N);
  printf("%d\n", N*(N + 1)/2);
  
  return 0;
}
### Prompt

Your challenge is to write a cpp solution to 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 <stdio.h>

int main() 
{
  int N;
  scanf("%d", &N);
  printf("%d\n", N*(N + 1)/2);
  
  return 0;
}
```