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

typedef unsigned long long ll;
const ll x = 1e18;

int main(){
    int n;
    cin >> n;

    ll b[n];
    for(int i = 0; i < n; i++)  cin >> b[i];

    for(int i = 0; i < n; i++){
        if(i%2){
            if(b[i] >= b[i-1]){
                cout << "-1" << endl;
                return 0;
            }
        }else{
            if(b[i] == 1){
                cout << "-1" << endl;
                return 0;
            }
        }
    }

    vector<ll> ans(n+1);
    ll first = 1;
    while(1){
        if(first <= 0 || first >= b[0]){
            cout << "-1" << endl;
            return 0;
        }

        ans[0] = first;
        int i;
        for(i = 0; i < n; i++){
            if(i%2){
                ll tmp = ans[i]-b[i];
                if(tmp <= 0){
                    first += -tmp+1;
                    break;
                }
                ans[i+1] = tmp;
            }else{
                ll tmp = b[i]-ans[i];
                if(tmp <= 0){
                    first += -tmp+1;
                    break;
                }
                ans[i+1] = tmp;
            }
        }

        if(i == n)  break;
    }

    cout << n+1 << endl;
    for(ll i : ans) cout << i << endl;
    
    return 0;
}