#include <iostream>
#include <fstream>
#include <cstdio>
#include <vector>
#define MMAX 500005
#define NMAX 100005
using namespace std;
struct vecini{
	int nod;
	int muchie;
};
int f[MMAX];
vector <vecini> v[NMAX];
int st[MMAX];
int raspuns[MMAX];
int main()
{
	FILE *fin=fopen("ciclueuler.in","r");
	ofstream fout("ciclueuler.out");
	int i,N,M,x,y,k,nr_elem=0,ok,varf;
	vecini a;
	fscanf(fin,"%d%d",&N,&M);
	for(i=1;i<=M;i++){
		fscanf(fin,"%d%d",&x,&y);
		a.nod=y;
		a.muchie=i;
		v[x].push_back(a);
		a.nod=x;
		v[y].push_back(a);
	}
	for(i=1;i<=N;i++){
		if(v[i].size()%2==1){
			fout<<"-1";
			return 0;
		}
	}
	/*for(i=1;i<=N;i++){
		for(vector <vecini> :: iterator it=v[i].begin();it!=v[i].end();it++){
			a=*it;
			fout<<a.nod<<" ";
		}
		fout<<"\n";
	}*/
	k=1;
	st[k]=1;
	while(k>0){
		varf=st[k];
		ok=0;
		for(vector <vecini>:: iterator it=v[varf].begin();it!=v[varf].end() && ok==0;it++){
			a=*it;
			if(f[a.muchie]==0){
				f[a.muchie]=1;
				k++;
				st[k]=a.nod;
				ok=1;
			}
		}
		if(ok==0){
			nr_elem++;
			raspuns[nr_elem]=st[k];
			k--;
		}
	}
	if(nr_elem>M+1){
		fout<<"-1";
		return 0;
	}
	for(i=2;i<=nr_elem;i++){
		fout<<raspuns[i]<<" ";
	}
    return 0;
}