// By Stefan Radu

#include <algorithm>
#include <fstream>
#include <iomanip>
#include <cassert>
#include <vector>
#include <string>
#include <cctype>
#include <queue>
#include <deque>
#include <cmath>
#include <stack>
#include <map>
#include <set>

using namespace std;

#define sz(x) (int)(x).size()

typedef pair < int, int > pii;
typedef long long ll;
typedef long double ld;
typedef unsigned int ui;
typedef unsigned long long ull;

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

struct Elem {
  Elem(int _n, int c): n(_n), cnt(c) {}
  int n, cnt;
};

void euler(int curNode, vector < vector < Elem > > &gr, vector < bool > &u) {

  while (sz(gr[curNode])) {

    auto aux = gr[curNode].back();
    if (u[aux.cnt]) {
      cout << aux.n << ' ';
      gr[curNode].pop_back();
      continue;
    }

    u[aux.cnt] = true;
    gr[curNode].pop_back();
    euler(aux.n, gr, u);
  }
}

void dfs(int curNode, vector < bool > &used, vector < vector < Elem > > &gr) {

  used[curNode] = true;
  for (auto x : gr[curNode]) {
    if (used[x.n]) continue;
    dfs(x.n, used, gr);
  }
}

int main() {

#ifdef STEF
  freopen("input", "r", stdin);
  freopen("output", "w", stdout);
#endif

  ios::sync_with_stdio(false);
  cin.tie(0);cout.tie(0);

  int n, m;
  cin >> n >> m;

  vector < int > deg(n + 1);
  vector < vector < Elem > > gr(n + 1);

  int cnt = 0;
  for (int i = 0; i < m; ++ i) {
    int a, b;
    cin >> a >> b;
    ++ deg[a];
    ++ deg[b];
    ++ cnt;
    gr[a].emplace_back(b, cnt);
    gr[b].emplace_back(a, cnt);
  }

  vector < bool > used(n);
  dfs(1, used, gr);
  for (int i = 1; i <= n; ++ i) {
    if (used[i] == 0) {
      cout << -1 << '\n';
      return 0;
    }
  }

  vector < bool > u(m + 1);

  int imp = 0;
  for (int i = 1; i <= n; ++ i) if (deg[i] & 1) ++ imp;

  if (imp == 0) {
    euler(1, gr, u);
  }
  else cout << -1 << '\n';
}