题目:http://acm.hdu.edu.cn/showproblem.php?pid=1001
import java.util.Scanner;
public class Main{
public static void main(String[] args) {
Scanner cin= new Scanner(System.in);
int sum;
while(cin.hasNextInt())
{
sum=cin.nextInt();
if((sum%2)==0)
System.out.println(sum/2*(sum+1));
else
System.out.println((sum+1)/2*sum);
System.out.println();
}
cin.close();//关闭输入流,关闭所有。
}
}