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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <vector>
using namespace std;

int main() {
	int n;
	cin>>n;
	int a[101];
	for (int i=1; i<=n; i++)
		cin>>a[i];

	vector<int> ans;
	for(; n>0; n--) {
		int pos = n;
		while(pos > 0 && a[pos] != pos)
			pos--;
		if (pos > 0) {
			ans.push_back(pos);
			while(pos+1 <= n) {
				a[pos] = a[pos+1];
				pos++;
			}
		}else
			break;
	}
	if (n)
		cout<<-1<<endl;
	else {
		for (int i=ans.size()-1; i>=0; i--)
			cout<<ans[i]<<" ";
		cout<<endl;
	}
	return 0;
}