#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#define pb push_back
using namespace std;

ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");

int n,aux;
vector < vector < int > > v;
vector < int > grad;
vector < int >::iterator it;

void citire()
{
    int m,x,y;
    in>>n>>m;
    v.resize(n+1);
    grad.resize(n+1);
    for(int i=1; i<=m; i++)
    {
        in>>x>>y;
        v[x].pb(y);
        v[y].pb(x);
        grad[x]++;
        grad[y]++;
    }
}

bool eGrafEulerian()
{
    for(int i=1; i<=n; i++)
        if(grad[i]%2)
            return false;
    return true;
}

void cicluEulerian()
{
    stack < int > stiva;
    int aux;
    vector < int > :: iterator it;
    stiva.push(1);

    while(!stiva.empty())
    {
        if(!v[stiva.top()].empty())
        {
            aux = v[stiva.top()].back();
            v[stiva.top()].pop_back();

            for(it=v[aux].begin(); *it!=stiva.top(); it++);
            *it = v[aux].back();
            v[aux].pop_back();

            stiva.push(aux);
        }
        else
        {
            if(stiva.size() != 1)
                out<<stiva.top()<<' ';
            stiva.pop();
        }
    }
}

int main()
{
    citire();
    if(eGrafEulerian())
        cicluEulerian();
    else
        out<<"-1";
    return 0;
}