#include <bits/stdc++.h>

int n;
long xs[112345];
long ys[112345];

int main() {
  scanf("%d", &n);
  for(int i = 0; i < n; ++i) {
    scanf("%ld", &xs[i]);
  }

  ys[0] = 1;
  int prev = 1;
  for(int i = 0; i < n; ++i) {
    long y = i % 2 == 0 ? xs[i] - prev : prev - xs[i];
    ys[i+1] = y;
    prev = y;
  }

  bool check = true;
  for(int i = 0; i < n + 1; ++i) {
    if( ys[i] <= 0 ) check = false;
  }

  if( check ) {
    printf("%d\n", n + 1);
    for(int i = 0; i < n + 1; ++i) {
      printf("%ld\n", ys[i]);
    }
  }
  else {
    printf("-1\n");
  }
      

  return 0;
}