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

#define NMAX 100000
#define MMAX 500000

using namespace std;

struct muchie {
  int to ;
  int ind ;
};

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

int main() {


  FILE *fin, *fout ;
  fin = fopen ("ciclueuler.in", "r") ;
  fout = fopen("ciclueuler.out", "w" ) ;
  int n, m, u, u2, i, e, ok, nod ;
  muchie elem ;
  fscanf (fin, "%d%d", &n, &m ) ;
  for (i = 0 ; i < m ; i++ ) {
    fscanf (fin, "%d%d", &u, &u2 ) ;
    g[u].push_back({u2, i}) ;
    g[u2].push_back({u, i}) ;
  }
  ok = 0 ;
  for (i = 1 ; i <= n ; i++ ) {
    if (g[i].size() % 2 != 0 )
      ok = 1 ;
  }
  if (ok == 1 )
    fprintf (fout, "-1" ) ;
  else {
    st.push(1) ;
    e = 0 ;
    while (!st.empty()) {
      nod = st.top() ;
      if (g[nod].size() > 0 ) {
          elem = g[nod].back() ;
          g[nod].pop_back() ;
          if (viz[elem.ind] == 0 ) {
            viz[elem.ind] = 1 ;
            st.push(elem.to) ;
          }
      }
      else {
        euler[e++] = st.top() ;
        st.pop() ;
      }
    }
    for (i = 0 ; i < e-1 ; i++ )
      fprintf (fout, "%d ", euler[i] ) ;
  }

  return 0;
}