#include <iostream>
using namespace std;

int main(){
  int n;
  cin >> n;
  if(n == 1){
    int b;
    cin >> b;
    if(b == 1){
      cout << -1 << endl;
      return 0;
    }
    cout << 2 << endl;
    cout << 1 << endl;
    cout << b-1 << endl;
    return 0;
  }
  int *a = new int[n+2], *b = new int[n+1];
  for (int j = 1; j <= n; ++j) cin >> b[j];

  int flag = 1;
  for(a[2] = b[2] + 1; a[2] < b[1]; ++a[2]){
    flag = 1;
    a[1] = b[1] - a[2];
    a[3] = a[2] - b[2];
    int i = 3;
    for (; i <= n && flag; ++i){
      if(i%2 == 1){
        a[i+1] = b[i] - a[i];
      } else {
        a[i+1] = a[i] - b[i];
      }
      flag = a[i+1] >= 1;
    }
    if(flag) break;
  }

  if(flag){
    cout << n+1 << endl;
    for(int i = 1; i <= n+1; i++){
      cout << a[i] << endl;
    }
  } else {
    cout << -1 << endl;
  }
  
  return 0;
}