#include<iostream.h>
#include<stdio.h>
#include<math.h>
int main()
{ int  n,i,j,k,p,v[25000],x;
  freopen("sume.in", "rt", stdin);
  freopen("sume.out", "wt", stdout);
  cin>>p;
  if(sqrt(1+8*p)!=(int)sqrt(1+8*p)) cout<<-1<<endl;
  else
   {n=(1+sqrt(1+8*p))/2; cout<<n<<endl;
    for( i=1;i<=p;i++)
      cin>>v[i];
    for(i=j=1,k=n-1;i<n;i++,k--)
    { x=(v[j]+v[j+1]-v[j+k])/2; cout<<x<<' ';
      j+=k;
    }
    cout<<v[p]-x<<endl;
    }
   return 0;
  }