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: Wrong Answer)

#include<bits/stdc++.h>
using namespace std;
namespace io{
    const int l=1<<20;
    char buf[l],*s,*t,c;
    inline void gc(){
        if(s==t){
            t=(s=buf)+fread(buf,1,l,stdin);
            c=s==t?EOF:*s++;
        }else c=*s++;
    }
    template<class IT>inline void gi(IT &x){
        x=0;gc();while(c<'0'||c>'9')gc();
        while('0'<=c&&c<='9'){x=(x<<1)+(x<<3)+(c^48);gc();}
    }
    char buf0[20];int a;
    template<class IT>inline void pi(IT x){
        if(x<0){putchar('-');x=-x;}
        do buf0[++a]=x%10+48;while(x/=10);
        while(a)putchar(buf0[a--]);
        putchar('\n');
    }
};
using io::gi;
using io::pi;
typedef unsigned int ui;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<int,ll > pil;
typedef pair<ll ,int> pli;
typedef pair<ll ,ll > pll;
typedef vector<int> vi;
typedef vector<ll > vl;
#define pque priority_queue
#define rep(i,l,r) for(i=(l);i<=(r);++i)
#define per(i,l,r) for(i=(l);i>=(r);--i)
#define REP(i,l,r) for(i=(l);i< (r);++i)
#define PER(i,l,r) for(i=(l);i> (r);--i)
#define mp make_pair
#define pb push_back
#define pf push_front
#define pob pop_back
#define pof pop_front
#define fi first
#define se second
template<class IT>inline void cmax(IT &a,IT b){if(a<b)a=b;}
template<class IT>inline void cmin(IT &a,IT b){if(b<a)a=b;}
const int N=105;
vi e[N];
int l[N];
void dfs(int v,int d){
	if(d)printf("%d\n",d);++d;
	int s=e[v].size();
	while(s--)dfs(e[v][s],d);
}
int main(){
    //freopen("a.in","r",stdin);
    //freopen("a.out","w",stdout);
    int n,i,a,mx=0;
    scanf("%d",&n);
    rep(i,1,n){
		scanf("%d",&a);
		if(a>mx+1){puts("-1");return 0;}
		else{e[l[a-1]].pb(l[a]=i);cmax(mx,a);}
	}
	dfs(0,0);
    return 0;
}