/*-------------
 Ex7_4.java
 課題5の解答例
 --------------*/

package jp_bunkyo;

import java.util.Scanner;

public class Ex7_4 {
	public static void main(String[] args) {
		Scanner stdin = new Scanner(System.in);
		int i, sum, num;

		System.out.print("1+2+…+num を求めるよ. num = ? > ");
		num = stdin.nextInt();

		if ( num < 0 ) {
			System.out.println("そんなのゆるさねー");
			return;
		}

		sum = 0;
		for ( i = 1; i <= num; i++ ) {
			sum += i;	// 「sum = sum + i;」 の簡略形
		}
		System.out.println(" 1 + 2 + … + " + num + " = " + sum + " だよ．");
	}
}