#include <bits/stdc++.h>
#include <fstream>
#include <vector>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

vector<list<int>> adj;
vector<int> ans;

void cycle(int u) {
  while (!adj[u].empty()) {
    int v = adj[u].front();
    adj[u].pop_front();
    auto it = find(adj[v].begin(), adj[v].end(), u);
    adj[v].erase(it);
    cycle(v);
  }
  ans.push_back(u);
}
int main() {
  int n, m;
  fin >> n >> m;
  adj.resize(n + 1);
  for (int i = 0; i < m; i++) {
    int x, y;
    fin >> x >> y;
    adj[x].push_back(y);
    adj[y].push_back(x);
  }
  for (int i = 1; i < adj.size(); i++)
    if (adj[i].size() % 2 == 1 || adj[i].size() == 0) {
      fout << -1;
      return 0;
    }
  cycle(1);
  for (int i = 0; i < ans.size() - 1; i++)
    fout << ans[i] << " ";
}