#include <iostream>
#include <fstream>
#include <queue>
#include <vector>
using namespace std;
ifstream f ("ciclueuler.in");
ofstream g ("ciclueuler.out");
int n,m;
vector<int>adiacenta[100001],rasp;
pair<int,int> muchii[500001];
queue<int>q;
int fr[500001],grade[100001];
void citire()
{
    f >> n >> m;
    for(int i = 1; i<=m; i++)
    {
        int x,y;
        f >> x >> y;
        adiacenta[x].push_back(i);
        adiacenta[y].push_back(i);
        grade[x]++;
        grade[y]++;
        muchii[i] = {x,y};
    }
}
void verificare()
{
    for(int i = 1; i<=n; i++)
        if(grade[i]%2 == 1)
        {
            g << -1;
            exit(0);
        }
}
void alg()
{
    q.push(muchii[1].first);
    while(!q.empty())
    {
        int nod_curent = q.front();
        rasp.push_back(nod_curent);
        q.pop();

        if(adiacenta[nod_curent].size() == 0)
            continue;

        while(adiacenta[nod_curent].size()!= 0 && fr[adiacenta[nod_curent].back()]==1)
        {
            adiacenta[nod_curent].pop_back();
        }
        if(adiacenta[nod_curent].size() == 0)
            continue;

        int muchie_curenta = adiacenta[nod_curent].back();
        adiacenta[nod_curent].pop_back();

        fr[muchie_curenta] = 1;
        if(muchii[muchie_curenta].first == nod_curent)
        {
            q.push(muchii[muchie_curenta].second);
        }
        else
            q.push(muchii[muchie_curenta].first);

    }
}
int main()
{
    citire();
    alg();
    for(int i = 0; i<rasp.size()-1; i++)
        g << rasp[i]<< " ";
}