#include <unordered_set>
#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

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

int n, x;
unordered_set < long long > s;
vector < long long > sol;

int main()
{
  in >> n;
  in >> x;
  for(int i = 1; i < n; i++) {
    int v, va;
    in >> v;
    va = v;
    v -= x;
    if(s.find(v) == s.end()) {
      s.insert(v);
      sol.push_back(v);
      x = va;
    } else {
      break;
    }
  }

  out << sol.size() << '\n';
  for(int i = 0; i < sol.size(); i++)
    out << sol[i] << '\n';

  in.close();
  out.close();
  return 0;
}