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

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

#define NMAX 100000
#define NRM 500000
typedef  pair<int, int> PII;

int n, m;
bool sel[NRM + 1];      //ce muchii vizitez;
vector<PII> G[NRM + 1];
vector<int> ans;

static inline bool IsEuler() {
  int ok = 1;
  for(int i = 1; i <= n; i++)
    if(G[i].size() % 2 == 1)
      ok = 0;
  return ok;
}

int main() {
  fin >> n >> m;
  for(int i = 1; i <= m; i++) {
    int x, y;

    fin >> x >> y;
    G[x].push_back({y, i}); //unde merg si a cata muchie e;
    G[y].push_back({x, i});
  }

  if(!IsEuler())
    fout << -1;
  else {
    stack<int> ST;
    ST.push(1);
    while(!ST.empty()) {
      int nod = ST.top();
      if(G[nod].size()) { //daca mai am vecini;
        int x = G[nod].back().first;
        int muchie = G[nod].back().second;
        G[nod].pop_back();
        if(!sel[muchie]) {
          sel[muchie] = 1;
          ST.push(x);
        }
      }else {
        ST.pop();
        ans.push_back(nod);
      }
    }
    ans.pop_back();
    for(auto e : ans)
      fout << e << " ";
  }

  return 0;
}