#include <fstream>
#include <vector>

using namespace std;

ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

const int N = 1e5 + 5;
const int M = 5e5 + 5;

int a[M], b[M], grad[N];
vector<int> gr[N];
bool used[M], afisat;

void euler(int nod) {
  for (auto muchie : gr[nod])
    if (!used[muchie]) {
      used[muchie] = true;
      if (a[muchie] == nod) euler(b[muchie]);
      else euler(a[muchie]);
    }
  if (afisat ^ (nod == 1))
    cout << nod << " ";
  afisat = true;
}

int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; ++i) {
    cin >> a[i] >> b[i];
    gr[a[i]].push_back(i);
    gr[b[i]].push_back(i);
    ++grad[a[i]], ++grad[b[i]];
  }
  cin.close();
  for (int i = 1; i <= n; ++i)
    if (grad[i] & 1) {
      cout << "-1\n";
      cout.close();
      return 0;
    }
  euler(1);
  cout.close();
  return 0;
}