Where is my problem ?

import java.io.*;
import java.util.*;
/*
有关算法的任务
*/

public class Solution {
    public static void main(String[] args) throws Exception {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        int maximum =0 ;
        int number = Integer.parseInt(reader.readLine());

        if(number>0){
        //在此编写你的代码
            int [] num = new int[number];
            int max = 0;

            for(int i = 0; i<=number-1; i++){
                num[i] = Integer.parseInt(reader.readLine());
            }

            for(int j = 0;j<=num.length-2;j++){
                max = j;

                for(int k =j+1;k<=num.length-1;k++){
                    if(num[max]<num[k]){
                        max = k;
                    }
                    int temp = num[j];
                    num[j] = num [max];
                    num[max] = temp;
                }
            }

            maximum = num[0];
            System.out.println(maximum);
        }
    }
}