NYOJ-sum of all integer numbers

NYOJ-sum of all integer numbers

sum of all integer numbers

描述

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

輸入

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

輸出

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

樣例輸入

3

樣例輸出

6

代碼:

#include
#include
int main()
{
	int n;
	while(~scanf("%d",&n))
	{
		if(n==0)
		{
			printf("1\n");
			continue;
		}
		int k=1,t=0;  
		if(n<0)
		k=-1,t=1;
		n=abs(n);
		if(n&1)
		printf("%d\n",((n+1)>>1)*n*k+t);
		else
		printf("%d\n",(n>>1)*(n+1)*k+t);
	   
	}
	return 0;
}