Problem:
Score : 400 points

Problem Statement

Snuke has an empty sequence a.

He will perform N operations on this sequence.

In the i-th operation, he chooses an integer j satisfying 1 \leq j \leq i, and insert j at position j in a (the beginning is position 1).

You are given a sequence b of length N. Determine if it is possible that a is equal to b after N operations. If it is, show one possible sequence of operations that achieves it.

Constraints

All values in input are integers.

1 \leq N \leq 100

1 \leq b_i \leq N

Input

Input is given from Standard Input in the following format:

N
b_1 \dots b_N

Output

If there is no sequence of N operations after which a would be equal to b, print -1.
If there is, print N lines. In the i-th line, the integer chosen in the i-th operation should be printed. If there are multiple solutions, any of them is accepted.

Sample Input 1

3
1 2 1

Sample Output 1

1
1
2

In this sequence of operations, the sequence a changes as follows:

After the first operation: (1)

After the second operation: (1,1)

After the third operation: (1,2,1)

Sample Input 2

2
2 2

Sample Output 2

-1

2 cannot be inserted at the beginning of the sequence, so this is impossible.

Sample Input 3

9
1 1 1 2 2 1 2 3 2

Sample Output 3

1
2
2
3
1
2
2
1
1

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Time Limit Exceeded)

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

	public static void main(String args[]) {

		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		List<Integer> b = new ArrayList<>();

		for(int i=0;i<N;i++) {
			b.add(sc.nextInt());
		}

		List<Integer> ans = listsearch(b,new ArrayList<Integer>());
		if(ans.size() == 0) {
			System.out.println(-1);
		}else {
			for(int i=ans.size()-1;i>=0;i--) {
				System.out.println(ans.get(i));
			}
		}

	}

	public static List<Integer> listsearch(List<Integer> b,List<Integer> ans) {

		if(b.size() == 0) return ans;

		List<Integer> b_temp;
		List<Integer> ans_temp;

		for(int i=b.size()-1;i>=0;i--) {
			if(b.get(i) == i+1) {
				b_temp = new ArrayList<>(b);
				ans_temp = new ArrayList<>(ans);
				b.remove(i);
				ans.add(i+1);
				List<Integer> c = listsearch(b,ans);
				if(c.size() != 0) {
					return c;
				}else {
					b = b_temp;
					ans = ans_temp;
				}
			}
		}
		return new ArrayList<Integer>();
	}
}