#include <stdio.h>
#include <vector>
#include <queue>
#include <stack>

#define maxdim 100005

using namespace std;

int n, m;
int viz[maxdim], viz_edge[5 * maxdim];
vector<pair<int, int>> G[maxdim];
stack<int> st;
vector<int> solution;

void dfs(int nod) {
  viz[nod] = 1;
  for (auto &p : G[nod]) {
    if (!viz[p.first]) {
      dfs(p.first);
    }
  }
}

int valid() {
  dfs(1);
  for (int i = 1; i <= n; ++i) {
    if (G[i].size() % 2 || !viz[i]) {
      return 0;
    }
  }
  return 1;
}

int euler() {
  if (!valid()) {
    return 0;
  }
  st.push(1);
  while (!st.empty()) {
    int nod = st.top();
    while (!G[nod].empty() && viz_edge[G[nod].back().second]) {
      G[nod].pop_back();
    }
    if (G[nod].empty()) {
      st.pop();
      solution.push_back(nod);
      continue;
    }
    viz_edge[G[nod].back().second] = 1;
    st.push(G[nod].back().first);
  }
  return 1;
}

int main() {
  freopen("ciclueuler.in", "r", stdin);
  freopen("ciclueuler.out", "w", stdout);
  
  scanf("%d %d", &n, &m);
  for (int i = 1; i <= m; ++i) {
    int x, y; scanf("%d %d", &x, &y);
    G[x].push_back(make_pair(y, i));
    G[y].push_back(make_pair(x, i));
  }

  if (!euler()) {
    printf("-1\n");
  } else {
    solution.pop_back();
    for (int nod : solution) {
      printf("%d ", nod);
    }
    printf("\n");
  }

  return 0;
}