import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.StringTokenizer;

public class Main {

    static BufferedReader in;
    static PrintWriter out;
    static StringTokenizer tok;

    void solve() throws IOException {
        int n = ni();
        long[] b = nla(n);

        long l = 1;
        long h = b[0] - 1;

        for (int i = 0; i < n; i++) {
            if (i % 2 == 0) {
                long tl = b[i] - h;
                long th = b[i] - l;
                l = tl;
                h = th;
            } else {
                long tl = l - b[i];
                long th = h - b[i];
                l = tl;
                h = th;
            }

            if (h <= 0) {
                out.println(-1);
                return;
            }

            l = Math.max(l, 1);
        }

        ArrayList<Long> list = new ArrayList<>();
        list.add(h);
        for (int i = n - 1; i >= 0; i--) {
            if (i % 2 == 0) {
                list.add(b[i] - list.get(n - 1 - i));
            } else {
                list.add(b[i] + list.get(n - 1 - i));
            }
        }

        out.println(n + 1);
        for (int i = n; i >= 0; i--) {
            out.println(list.get(i));
        }
    }

    String ns() throws IOException {
        while (!tok.hasMoreTokens()) {
            tok = new StringTokenizer(in.readLine(), " ");
        }
        return tok.nextToken();
    }

    int ni() throws IOException {
        return Integer.parseInt(ns());
    }

    long nl() throws IOException {
        return Long.parseLong(ns());
    }

    double nd() throws IOException {
        return Double.parseDouble(ns());
    }

    String[] nsa(int n) throws IOException {
        String[] res = new String[n];
        for (int i = 0; i < n; i++) {
            res[i] = ns();
        }
        return res;
    }

    int[] nia(int n) throws IOException {
        int[] res = new int[n];
        for (int i = 0; i < n; i++) {
            res[i] = ni();
        }
        return res;
    }

    long[] nla(int n) throws IOException {
        long[] res = new long[n];
        for (int i = 0; i < n; i++) {
            res[i] = nl();
        }
        return res;
    }

    public static void main(String[] args) throws IOException {
        in = new BufferedReader(new InputStreamReader(System.in));
        out = new PrintWriter(System.out);
        tok = new StringTokenizer("");
        Main main = new Main();
        main.solve();
        out.close();
    }
}