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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCorder
{
	public class Program
	{
		static void Main(string[] args)
		{
			int n = int.Parse(Console.ReadLine());
			var b = Console.ReadLine().Split(' ').Select(int.Parse).ToList();
			List<int> c = new List<int>();
			for (int i = 0; i < n; i++) {
				for (int j = n - 1 - i; j >= 0; j--) {
					if (b[j] == j + 1) {
						c.Add(j + 1);
						b.RemoveAt(j);
						break;
					}
				}
			}

			if (b.Count != 0) {
				Console.WriteLine($"{-1}");
				return;
			}

			StringBuilder sb = new StringBuilder();
			for (int i = c.Count - 1; i >= 0; --i) {
				sb.AppendLine($"{c[i]}");
			}

			Console.WriteLine(sb.ToString());
		}
	}
}