import java.io.*;
import java.util.*;


public class Main_yukicoder451 {

	private static Scanner sc;
	private static Printer pr;

	private static void solve() {
		int n = sc.nextInt();

		long[] b = new long[n];
		for (int i = 0; i < n; i++) {
			b[i] = sc.nextLong();
		}

		long[] max = new long[n + 1];
		Arrays.fill(max, Long.MAX_VALUE);

		for (int i = 0; i < n; i++) {
			if (i % 2 == 0) {
				max[i] = Math.min(max[i], b[i] - 1);
				max[i + 1] = Math.min(max[i + 1], b[i] - 1);
			} else {
				long tmp = b[i - 1] - b[i];
				b[i] = tmp;
				if (tmp < 2) {
					pr.println(-1);
					return;
				}
				max[i - 1] = Math.min(max[i - 1], tmp - 1);
				max[i + 1] = Math.min(max[i + 1], tmp - 1);
			}
		}

		for (int i = 0; i <= n; i++) {
//			pr.println(max[i]);
			if (max[i] < 1) {
				pr.println(-1);
				return;
			}
		}

//		long l = 0;
//		long r = 1_000_000_000_000_000_000L;
		long r = max[0];
		/*
		while (r - l > 1) {
			long mid = l + (r - l) / 2;

			if (f(mid, b)) {
				r = mid;
			} else {
				l = mid;
			}
		}
		*/
		if (f(1, b)) {
			r = 1;
		} else if (f(max[0], b)) {
			r = max[0];
		} else {
//			r = max[0] / 2;
			pr.println(-1);
			return;
		}

		if (f(r, b)) {
			long[] a = new long[n + 1];
			a[0] = r;
			for (int i = 1; i <= n; i++) {
				if (i % 2 == 1) {
					a[i] = b[i - 1] - a[i - 1];
				} else {
					a[i] = b[i - 1] - a[i - 2];
				}
			}

			pr.println(n + 1);
			for (int i = 0; i <= n; i++) {
				pr.println(a[i]);
			}
		} else {
			pr.println(-1);
		}
	}

	private static boolean f(long mid, long[] b) {
		int n = b.length;

		long[] a = new long[n + 1];
		a[0] = mid;
		for (int i = 1; i <= n; i++) {
			if (i % 2 == 1) {
				a[i] = b[i - 1] - a[i - 1];
			} else {
				a[i] = b[i - 1] - a[i - 2];
			}

			if (a[i] <= 0) {
				return false;
			}
		}

		return true;
	}

	// ---------------------------------------------------
	public static void main(String[] args) {
		sc = new Scanner(System.in);
		pr = new Printer(System.out);

		solve();

		pr.close();
		sc.close();
	}

	@SuppressWarnings("unused")
	private static class Scanner {
		BufferedReader br;

		Scanner (InputStream in) {
			br = new BufferedReader(new InputStreamReader(in));
		}

		private boolean isPrintable(int ch) {
			return ch >= '!' && ch <= '~';
		}

		private boolean isCRLF(int ch) {
			return ch == '\n' || ch == '\r' || ch == -1;
		}

		private int nextPrintable() {
			try {
				int ch;
				while (!isPrintable(ch = br.read())) {
					if (ch == -1) {
						throw new NoSuchElementException();
					}
				}

				return ch;
			} catch (IOException e) {
				throw new NoSuchElementException();
			}
		}

		String next() {
			try {
				int ch = nextPrintable();
				StringBuilder sb = new StringBuilder();
				do {
					sb.appendCodePoint(ch);
				} while (isPrintable(ch = br.read()));

				return sb.toString();
			} catch (IOException e) {
				throw new NoSuchElementException();
			}
		}

		int nextInt() {
			try {
				// parseInt from Integer.parseInt()
				boolean negative = false;
				int res = 0;
				int limit = -Integer.MAX_VALUE;
				int radix = 10;

				int fc = nextPrintable();
				if (fc < '0') {
					if (fc == '-') {
						negative = true;
						limit = Integer.MIN_VALUE;
					} else if (fc != '+') {
						throw new NumberFormatException();
					}
					fc = br.read();
				}
				int multmin = limit / radix;

				int ch = fc;
				do {
					int digit = ch - '0';
					if (digit < 0 || digit >= radix) {
						throw new NumberFormatException();
					}
					if (res < multmin) {
						throw new NumberFormatException();
					}
					res *= radix;
					if (res < limit + digit) {
						throw new NumberFormatException();
					}
					res -= digit;

				} while (isPrintable(ch = br.read()));

				return negative ? res : -res;
			} catch (IOException e) {
				throw new NoSuchElementException();
			}
		}

		long nextLong() {
			try {
				// parseLong from Long.parseLong()
				boolean negative = false;
				long res = 0;
				long limit = -Long.MAX_VALUE;
				int radix = 10;

				int fc = nextPrintable();
				if (fc < '0') {
					if (fc == '-') {
						negative = true;
						limit = Long.MIN_VALUE;
					} else if (fc != '+') {
						throw new NumberFormatException();
					}
					fc = br.read();
				}
				long multmin = limit / radix;

				int ch = fc;
				do {
					int digit = ch - '0';
					if (digit < 0 || digit >= radix) {
						throw new NumberFormatException();
					}
					if (res < multmin) {
						throw new NumberFormatException();
					}
					res *= radix;
					if (res < limit + digit) {
						throw new NumberFormatException();
					}
					res -= digit;

				} while (isPrintable(ch = br.read()));

				return negative ? res : -res;
			} catch (IOException e) {
				throw new NoSuchElementException();
			}
		}

		float nextFloat() {
			return Float.parseFloat(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			try {
				int ch;
				while (isCRLF(ch = br.read())) {
					if (ch == -1) {
						throw new NoSuchElementException();
					}
				}
				StringBuilder sb = new StringBuilder();
				do {
					sb.appendCodePoint(ch);
				} while (!isCRLF(ch = br.read()));

				return sb.toString();
			} catch (IOException e) {
				throw new NoSuchElementException();
			}
		}

		void close() {
			try {
				br.close();
			} catch (IOException e) {
//				throw new NoSuchElementException();
			}
		}
	}

	private static class Printer extends PrintWriter {
		Printer(PrintStream out) {
			super(out);
		}
	}
}