如何用java while loop实现：输入正整数，减去小于等于此数的正整偶数值

如，输入7，程序进行7-6-4-2，输出-5

谢谢谢谢！

import java.util.Scanner;

public class Test {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int i;
        if(n<=0){
            System.out.println("请输入正整数！");
        }else{
            if(n%2==0){//n是偶数
                i = n;
            }else{//n是奇数
                i = n-1;
            }
            while(i>0){
                n = n-i;
                i = i-2;
            }
            System.out.println(n);
        }
    }
}

public static void main(String[] args) {
   int n = 7;
   int num = n;
   while (n > 0){
      --n;
      if(n % 2 == 0){
         System.out.println(n);
         num -= n;
      }
   }
   System.out.println(num);
}

n-((n/2)*(n/2 + 1))