#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], eu;
bool viz[M];

void euler(const int& start) {
  stack<int> st;
  st.push(start);
  while (!st.empty()) {
    auto nod = st.top();
    while (!gr[nod].empty() && viz[gr[nod].back()])
      gr[nod].pop_back();
    if (gr[nod].empty()) {
      eu.push_back(nod);
      st.pop();
    } else {
      viz[gr[nod].back()] = true;
      if (nod == a[gr[nod].back()])
        st.push(b[gr[nod].back()]);
      else
        st.push(a[gr[nod].back()]);
    }
  }
  eu.pop_back();
}

int main() {
  ifstream cin("ciclueuler.in");
  ofstream cout("ciclueuler.out");
  int n, m, start;
  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]];
    start = a[i];
  }
  cin.close();
  for (int i = 1; i <= n; ++i)
    if (grad[i] % 2 == 1) {
      cout << "-1\n";
      cout.close();
      return 0;
    }
  euler(start);
  if (eu.size() != m) {
    cout << "-1\n";
    cout.close();
    return 0;
  }
  for (auto i: eu)
    cout << i << " ";
  cout.close();
  return 0;
}