#include<bits/stdc++.h>
#pragma comment(linker, "/STACK:16777216")#include<fstream>
using namespace std;
 
ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");
 
typedef struct lnod {
    int info;
    lnod *next;
}*nod;
 
int i,n,m,x,y,grad[100005];
bool viz[100005];
nod lda[100005];
 
void add(int x,nod &y) {
    nod p=new lnod;
    p->info=x;
    p->next=y;
    y=p;
}
 
void dfs(int x,int lvl) {
    while(lda[x])
    {
      int aux=lda[x]->info;
      lda[x]=lda[x]->next;
      nod p=lda[aux];
      if(p->info==x) lda[aux]=lda[aux]->next;
      else {
             while(p->next->info!=x) p=p->next;
             p->next=p->next->next;
           }
      dfs(aux,lvl+1);
    }
    if(lvl) cout<<x<<' ';
}
 
int main()
{
  ios_base::sync_with_stdio(0);
 
  for(cin>>n>>m;m;--m)
  {
    cin>>x>>y;
    add(x,lda[y]); ++grad[y];
    add(y,lda[x]); ++grad[x];
  }
 
  for(i=1;i<=n;++i)
  if(grad[i]&1) return cout<<"-1\n",0;
 
  dfs(1,0);
 
 return 0;
}