310 迴圈正偶數相加

import java.util.Scanner;
public class JPA310 {
    static Scanner keyboard = new Scanner(System.in);
    public static void main(String[] args) {
int n;
int sum=0;
do{
System.out.print("請輸入 n 的值(n>0，且為偶數):");
n = keyboard.nextInt();

}while(n<0||n%2==1);
for(int i = 0; i<=n;i=i+2){
sum+=i;
}
System.out.println("2+4+...+"+n+"="+sum);
    }
}