<swustoj>?id=606 Sum

链接http://acm.swust.edu.cn/problem/606/

#include <stdio.h>
int main()
{
    int x,sum;
    scanf("%d",&x);
       
    if(x==1)
    {
        sum=1;
    }
    else if(x>1)
    {
        sum=x*(x+1)/2;
    }
    else if(x==0)
    {
        sum=1;
    }
    else if(x<0)
    {
        sum=1-x*(x-1)/2;
    }
    printf("%d\n",sum);
       
    return 0;
}