#include<bits/stdc++.h>
using namespace std;

vector<long long> vect;
vector<long long> ans;
int main(){
	int n;
	cin >> n;
	for(int i = 0; i < n; i++){
		long long a;
		cin >> a;
		vect.push_back(a);
	}
	
	bool ok = true;
	for(int i = 0; i < n; i++){
		if(i % 2 == 0 && i == vect.size() - 1){
			if(vect[i] < vect[i + 1])ok = false;
		}
	}
	
	if(ok == false)cout << "-1" << endl;
	else{
		cout << n + 1 << endl;
		for(int i = 0; i < n; i++){
			cout << vect[i] << endl;
		}
		cout << 1 << endl;
	}
}