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: Accepted)

import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] b = new int[n];
    for(int i = 0; i < n; i++) {
      b[i] = sc.nextInt();
    }
    int f = 0;
    int[] ans = new int[n];
    for(int i = n - 1; i >= 0; i--) {
      int p = 0;
      int t = 0;
      for(int j = n - 1; j >= 0; j--) {
        if(b[j] == (j + 1)) {
          p = 1;
          ans[i] = (j + 1);
          t = j;
          break;
        }
      }
      if(p == 0) {
        f = 1;
        System.out.println(-1);
        break;
      } else {
        for(int j = t; j < n; j++) {
          if(j < n - 1) b[j] = b[j + 1];
          if(j == n - 1) b[j] = 0;
        }
      }
    }
    if(f == 0) {
      for(int i = 0; i < n; i++) {
        System.out.println(ans[i]);
      }
    }
  }
}