#include <fstream>
#define MAX 500001

using namespace std;

int x[MAX], aux[MAX], a[MAX];
int n, k = 0;

int main()
{
    int i, j, ok;
    ifstream fin("reguli.in");
    fin >> n;
    fin >> x[0];
    for (i = 1; i < n; i++)    
    {
        fin >> x[i];
        aux[i] = x[i]-x[i-1];
        ok = 0;
        for (j = 1; j < i; j++)
            if (aux[j] == aux[i])
            {
               ok = 1;
               break;
            }
        if (!ok) 
        {
            k++;
            a[k] = aux[i];
        }
    }
    
    ofstream fout("reguli.out");
    fout << k << "\n";
    for (i = 1; i <= k; i++)
        fout << a[i] << "\n";
    fout.close();
        
    fin.close();
    
}