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.*;

import static java.lang.System.*;

public class Main {
    static Scanner sc = new Scanner(System.in);

    public static void main(String[] args) {
        int N = ni();

        List<Integer> b = new ArrayList<>();
        for (int i = 0; i < N; i++) {
            b.add(sc.nextInt());
        }

        List<Integer> seq = new ArrayList<>();
        boolean canPick = true;
        while (canPick) {
            canPick = false;
            for (int i = b.size() - 1; i >= 0; i--) {
                if (b.get(i) == i + 1) {
                    b.remove(i);
                    seq.add(i + 1);
                    canPick = true;
                    break;
                }
            }
        }

        if (b.isEmpty()) {
            Collections.reverse(seq);
            for (int s : seq) {
                out.println(s);
            }
        } else {
            out.println(-1);
        }
    }

    static int ni() {
        return sc.nextInt();
    }

    static long nl() {
        return sc.nextLong();
    }

    static String ns() {
        return sc.next();
    }

    static int[] niarr(int N) {
        int[] a = new int[N];
        for (int i = 0; i < N; i++) {
            a[i] = sc.nextInt();
        }
        return a;
    }

    static long[] nlarr(int N) {
        long[] a = new long[N];
        for (int i = 0; i < N; i++) {
            a[i] = sc.nextLong();
        }
        return a;
    }
}