#include <fstream>
#include <vector>
#include <stack>

using namespace std;

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

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

int afla_vec(int nod) {
  while (!gr[nod].empty() && used[gr[nod].back()])
    gr[nod].pop_back();
  if (gr[nod].empty())
    return -1;
  int muchie = gr[nod].back();
  gr[nod].pop_back();
  used[muchie] = true;
  if (a[muchie] != nod) return a[muchie];
  return b[muchie];
}

void euler(int start) {
  stack<int> st;
  st.push(start);
  while (!st.empty()) {
    auto nod = st.top();
    int vec = afla_vec(nod);
    if (vec == -1) {
      ans.push_back(nod);
      st.pop();
    }
    else
      st.push(vec);
  }
}

int main() {
  ifstream cin("ciclueuler.in");
  ofstream cout("ciclueuler.out");
  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] % 2) {
      cout << "-1\n";
      cout.close();
      return 0;
    }
  euler(1);
  ans.pop_back();
  for (auto i : ans)
    cout << i << " ";
  cout.close();
  return 0;
}