#include<bits/stdc++.h>
#define maxn 500005
using namespace std;

ifstream fin("reguli.in");
ofstream fout("reguli.out");

int main()
{
    int n,v[maxn],x;
    vector <int> sol;
    fin>>n;
    for(int i=1;i<=n;i++)
        fin>>v[i];
    int s1=v[2]-v[1];
    sol.push_back(s1);
    x=v[2];
    for(int i=3;i<=n;i++)
    {
        if(v[i]-x!=s1)
            sol.push_back(v[i]-x);
        else
            break;
        x=v[i];
    }
    fout<<sol.size()<<"\n";
    for(int i=0;i<sol.size();i++)
        fout<<sol[i]<<"\n";
    return 0;
}