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: Runtime Error)

import java.util.*;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		boolean flag = false, imposible = false;		
		ArrayList<Integer> a = new ArrayList<Integer>();
		ArrayList<Integer> b = new ArrayList<Integer>();
		for(int i = 0; i < n; i++){
			b.add(sc.nextInt());
		}
		for(int i = 0; i < n; i++){
			for(int j = b.size() - 1; 0 <= j; j--){
				if(b.get(j) == j - 1){
					a.add(j);
					flag = true;
					break;
				}
			}
			if(flag == false){
				System.out.println(-1);
				imposible = true;
				break;
			}
			flag = false;
		}
		if(imposible == false){
			for(int i = a.size(); 0 <= i; i--){
				System.out.println(a.get(i));
			}
		}
	}
}