#include <cstdio>
#include <cctype>
#include <list>
#include <queue>
#define LIM 2000000
#define MAXN 100010
#define MAXM 500010

using namespace std;

FILE *fin;
int p=LIM-1;
char str[LIM];

inline void avans(){
  if(++p==LIM){
    fread(str, 1, LIM, fin);
    p=0;
  }
}

inline int getnr(){
  int nr=0;
  while(isdigit(str[p])==0)
    avans();
  while(isdigit(str[p])){
    nr=nr*10+str[p]-'0';
    avans();
  }
  return nr;
}

int sol[MAXM+1], s;
int vf[2*MAXM], M, lst[MAXN+1], next[2*MAXM], fol[MAXM];
int viz[MAXN+1], grad[MAXN+1], stiv[MAXM+1];

inline void add(int x, int y){
  vf[++M]=y;
  next[M]=lst[x];
  lst[x]=M;
}

inline void bfs(int nod){
  int q[MAXN], b, e, p;
  b=0; e=1; q[b]=nod;
  while(b<e){
    nod=q[b++];
    viz[nod]=1;
    p=lst[nod];
    while(p){
      if(viz[vf[p]]==0)
        q[e++]=vf[p];
      p=next[p];
    }
  }
}

void euler(int nod){
  int st=0, mu;
  stiv[st]=nod;
  while(st>=0)
    if(lst[stiv[st]]==0)
      sol[s++]=stiv[st--];
    else if(fol[(lst[stiv[st]]-1)/2])
      lst[stiv[st]]=next[lst[stiv[st]]];
    else{
      mu=lst[stiv[st]];
      lst[stiv[st]]=next[lst[stiv[st]]];
      fol[(mu-1)/2]=1;
      stiv[++st]=vf[mu];
    }
}

int main()
{
    FILE *fout;
    int n, m, i, x, y;
    fin=fopen("ciclueuler.in", "r");
    fscanf(fin, "%d%d", &n, &m);
    for(i=0; i<m; i++){
      x=getnr(); y=getnr();
      grad[x]++; grad[y]++;
      add(x, y);
      add(y, x);
    }
    fclose(fin);
    bfs(1);
    for(i=1, x=0; i<=n && x==0; i++)
      if((grad[i]&1) || viz[i]==0)
        x=1;
    fout=fopen("ciclueuler.out", "w");
    if(x)
      fprintf(fout, "-1\n");
    else{
      euler(1);
      for(i=0; i<s-1; i++)
        fprintf(fout, "%d ", sol[i]);
      fprintf(fout, "\n");
    }
    return 0;
}