九度OJ 1063 清华机试之整数和。

题目地址：http://ac.jobdu.com/problem.php?pid=1063

//九度OJ 1063 清华机试之整数和。//http://ac.jobdu.com/problem.php?pid=1063#include <stdio.h>#define MAXS 200int main(){int n,flag,sum;while(~scanf("%d",&n)){if(n>=0)flag=1;else{flag=-1;n=-n;}sum=n*(n+1)*3/2;printf("%d\n",flag*sum);}return 0;}