#include <fstream>
#define DIM 500010
using namespace std;

ifstream fin ("reguli.in");
ofstream fout ("reguli.out");
long long v[DIM],d[DIM];
long long dif;
int n,i,poz,k;
int main (){

    fin>>n;
    for (i=1;i<=n;i++)
        fin>>v[i];
    d[++k] = v[2]-v[1];
    for (i=2;i<n;i++){
        dif = v[i+1]-v[i];
        poz = (i%k)?(i%k):(k);
        if (d[poz] != dif)
            d[++k] = dif;
    }
    fout<<k<<"\n";
    for (i=1;i<=k;i++)
        fout<<d[i]<<"\n";

    return 0;
}