#include <iostream>
#include<cstdio>
#include<vector>
using namespace std;
const int N=100001;
const int M=5*N;
FILE*fin,*fout;
struct ajutormuchii{
  int dest;
  int id;
};
bool vizm[M];
bool vizn[N+5];
vector<ajutormuchii> gr[N];
int q[M];
int cnt=0;
void dfs_euler(int nod,int &cntafis){
  if(vizn[nod]==0){
    cnt++;
  }
  vizn[nod]=1;
  for(auto x:gr[nod]){
    if(vizm[x.id]==false){
      vizm[x.id]=true;
      dfs_euler(x.dest,cntafis);
    }
  }
  q[++cntafis]=nod;
}

const int SIZE=1<<15;
char buffer[SIZE];
int point=SIZE;
inline char adv(){
  if(point==SIZE){
    fread(buffer,1,SIZE,fin);
    point=0;
  }
  return buffer[point++];
}
inline int read(){
  char c;
  int x=0,sgn=1;
  c=adv();
  while(isdigit(c)==false && c!='-')
    c=adv();
  while(c=='-'){
    sgn*=-1;
    c=adv();
  }
  while(isdigit(c)){
    x=x*10+c-'0';
    c=adv();
  }
  return x*sgn;
}
int main()
{
  int n,m;
  fin=fopen("ciclueuler.in","r");
  fout=fopen("ciclueuler.out","w");
  n=read();
  m=read();
  int id=0;
  for(int i=1;i<=m;i++){
    int x,y;
    x=read();
    y=read();
    ++id;
    gr[x].push_back({y,id});
    gr[y].push_back({x,id});
  }
  for(int i=1;i<=n;i++){
    if(gr[i].size()%2==1){
        fprintf(fout,"-1\n");
      return 0;
    }
  }
  int c=0;
  dfs_euler(1,c);
  if(cnt==n){
    for(int i=1;i<=m;i++){
      fprintf(fout,"%d ",q[i]);
    }
  }
  else{
    fprintf(fout,"-1\n");
      return 0;
  }
  return 0;
}