#include <iostream>
#include <stack>
#include <vector>

#define NMAX 100000
#define MMAX 500000

using namespace std;

struct muchie {
  int to ;
  int poz ;
};

stack <int> s ;
vector <muchie> g [ NMAX + 1 ] ;
int viz [ MMAX + 1 ] ;
int euler [ MMAX + 1 ] ;
int e;

void dfs (int nod ) {
  for (auto elem : g[nod] ) {
    if (!viz[elem.poz]) {
      viz[elem.poz] = 1 ;
      dfs(elem.to) ;
    }
  }
  euler[e++] = nod ;
}

int main() {

  FILE *fin, *fout ;
  fin = fopen ("ciclueuler.in", "r" ) ;
  fout = fopen ("ciclueuler.out", "w" ) ;
  int n, m, i, u, v, ok, nod ;
  fscanf (fin, "%d%d", &n, &m ) ;
  for (i = 0 ; i < m ; i++ ) {
    fscanf (fin, "%d%d", &u, &v) ;
    g[u].push_back({v, i}) ;
    g[v].push_back({u, i}) ;
  }
  ok = 0 ;
  for (i = 1 ; i <= n ; i++ )
    if (g[i].size() % 2 == 1 )
      ok = 1 ;
  if (ok == 1 )
    fprintf (fout, "-1" ) ;
  else {
    e = 0 ;
    dfs(1) ;
    for (i = 0 ; i < e ; i++ )
      fprintf (fout, "%d ", euler[i] ) ;
  }
  return 0;
}