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

public class Hello
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = new List<int>();
        for (int i = 0; i < n; i++)
            a.Add(int.Parse(line[i]));
        getAns(a);
    }
    static void getAns(List<int> a)
    {
        var ans = new List<int>();
        while (a.Count() > 0)
        {
            var ac = a.Count();
            var find = false;
            for (int i = ac - 1; i >= 0; i--)
            {
                if (a[i] == i + 1)
                {
                    ans.Add(a[i]);
                    a.RemoveAt(i);
                    find = true;
                    break;
                }
            }
            if (!find) { Console.WriteLine(-1); return; }
        }
        ans.Reverse();
        var sb = new StringBuilder();
        foreach (var x in ans) sb.Append(string.Format("{0}\n", x));
        Console.Write(sb);
    }
}