題意：輸入n，求1~n之和。

import java.util.Scanner;
public class Main {

    public static void main(String[] args) {
        
        Scanner s=new Scanner(System.in);
        int n=0;
        int sum;
        while(s.hasNextInt())
        {
            sum=0;
            n=s.nextInt();
            for(int i=1;i<=n;i++)
            {
                sum+=i;
            }
            System.out.println(sum);
        System.out.println();    
        }        
    }    
}
 

#include <cstdio>

int main()
{
    int n;
    while (scanf("%d", &n) != EOF)
    {

        printf("%d\n\n", n%2 ? (n+1)/2*n: (n + 1)*(n/2));
    }
}

#include <cstdio>
#include <iostream>
using namespace std;

void main()
{
    int n;
    while (scanf("%d", &n) != EOF)
    {
        if (n & 1)
            n = (n + 1) / 2 * n;
        else
            n = n / 2 * (n + 1);
        printf("%d\n\n", n);
    }
}