Sum URAL - 1068

Your task is to find the sum of all integer numbers lying between 1 and Ninclusive.

Input

The input consists of a single integer N that is not greater than 10000 by it's absolute value.

Output

Write a single integer number that is the sum of all integer numbers lying between 1 and N inclusive.

Example

input	output
-3	-5

 

#include <stdio.h>

int main(){
    int n, sum;
    while(~scanf("%d", &n)){
        sum = 0;
        if(n < 1)
            sum = n*(1-n)/2 + 1;
        else sum = n*(n+1)/2;
        printf("%d\n", sum);
    }
    return 0;
}