尝试一下

这是标题

这是正文

import java.util.*;
public class one{
public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    sc.nextLine();
    int[] a =new int[n];
    for (int i = 0; i <n ; i++) {
        a[i] = sc.nextInt();
    }
    Arrays.sort(a);
    int c =0,k =0;
    long sum =0;
    for (int i = n-2; i >=0 ; i--) {
        if(c == 0 && (a[i] == a[i+1])){
            c = a[i];
            i--;
            continue;
        }
        if(c != 0 && k ==0 && (a[i] == a[i+1])){
            k =a[i];
            sum = c*k;
            System.out.println(sum);
            break;
        }
    }
    if(sum ==0){
        System.out.println(-1);
    }
    sc.close();
    }

}