#include <iostream>
#include <string>
#include <algorithm>
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
long long a[100010];
long long b[100010];
int main() {
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}
	for (int i = 0; i < n; i += 2) {
		if (a[i] < 2) {
			cout << "-1" << endl;
			return 0;
		}
		if (a[i] - a[i + 1] < 2) {
			cout << "-1" << endl;
			return 0;
		}
	}
	b[0] = 1;
	for (int i = 0; i < n; i++) {
		if (i % 2 == 0){
			b[i + 1] = a[i] - b[i];
		}
		else {
			b[i + 1] = b[i] - a[i];
		}
	}
	for (int i = 1; i <= n; i++) {
		if (b[i] <= 0) {
			cout << "-1" << endl;
			return 0;
		}
	}
	cout << n + 1 << endl;
	for (int i = 0; i <= n; i++) {
		cout << b[i] << endl;
	}
	return 0;
}