#include <iostream>
#include <math.h>
#include <fstream>


using namespace std;

int n,n1,s1=0,s2=0;
float delta,sol[25001], v[25001];
void citire ()
{
    ifstream f ("sume.in");
    f>> n ;
    for(int i= 1; i<= n ; i++ )
    {
        f>>v[i];
    }
}
void afisare (int k)
{
    ofstream g ("sume.out");
    if(k == 0 )
    {
        g<<-1;
        return;
    }
    g<<n1<<endl;
    for (int i =0; i <=n1-1; i++ )
    {
        g<<sol[i]<<" ";
    }

}
/*void testare()
{
    for(int i = 1,j=0; i <= n,j<=n1-1; i ++ ,j++)
    {
        s1=s1+v[i];
        s2=s2+sol[j];
    }



    if(s1%s2 == 0 )
        afisare(1);
    else
        afisare(0);
}*/
void sume ()
{
    delta=1+n*4*2;
    if(sqrt(delta)- int(sqrt(delta)) !=0 )
    {
        afisare(0);
        return;
    }
    n1=(1+sqrt(delta))/2;


    sol[0]=(v[1]+v[2] - v[n1])/2;

    for(int i =1 ; i<=n1-1; i++)
    {
        sol[i]=v[i]-sol[0];
    }
    //testare();
}

int main()
{
    citire();
    sume();
    return 0;
}