import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int T = in.nextInt();
            while (T-- > 0) {
                int n = in.nextInt();
                int moreThen2Count = 0;
                int maxCount = 0;
                for (int i=0;i<n;i++) {
                    int v = in.nextInt();
                    if (v > 1) {
                        moreThen2Count++;
                    }
                    maxCount = Math.max(maxCount, v);
                }
                
                if (n == 1) {
                    System.out.println(-1);
                } else if (moreThen2Count > 1) {
                    System.out.println(maxCount);
                } else {
                    System.out.println(maxCount-1);
                }
            }
        }
    }
}