不知道为什么wa

import java.util.Arrays;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int[] arr = new int[n + 1];
        for (int i = 1; i <= n; i++){
            arr[i] = scanner.nextInt();
        }
        Arrays.sort(arr);


        for (int i = 1;i<=n;i++){
            if (arr[i]!=i){
                System.out.print(i);
                break;
            }
        }
    }
}