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 <bits/stdc++.h>

using namespace std;

int num[105],ans[105];
bool in[105];

int main() {
  memset(in,1,sizeof(in));
  int n;
  scanf("%d",&n);
  for(int i=1;i<=n;i++) scanf("%d",&num[i]);
  for(int i=n;i>0;i--) {
  	int cur=0,s=0;
    for(int j=1;j<=n;j++)
      if (in[j]) {
      	s++;
      	if (num[j]==s) cur=j;
	  }
	if (cur&&num[cur]<=i) {
		ans[i]=num[cur];
		in[cur]=0;
	}
	else {
		puts("-1");
		return 0;
	}
  }
  for(int i=1;i<=n;i++) printf("%d\n",ans[i]);
  return 0;
}