#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream f ("tester.in");
ofstream g ("tester.out");
int n,m;
struct muchie
{
    int x,y;
    bool fr;
}muchii[500001];
stack<int>s;
vector<int>rasp;
vector<int>adiacenta[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);
        muchii[i] = {x,y,0};
    }
}
bool verificare()
{
    for(int i = 1; i<=n; i++)
    {
        if(adiacenta[i].size()%2 == 1)
            return 1;
    }
    return 0;
}

void alg()
{
    s.push(1);
    while(!s.empty())
    {
        int curent = s.top();
        if(adiacenta[curent].size()==0)
        {
            rasp.push_back(curent);
            s.pop();
        }
        else
        {
            int next_muchie = adiacenta[curent].back();
            adiacenta[curent].pop_back();
            if(muchii[next_muchie].fr == 0)
            {
                muchii[next_muchie].fr = 1;
                if(curent == muchii[next_muchie].x)
                    s.push(muchii[next_muchie].y);
                else
                    s.push(muchii[next_muchie].x);
            }
        }
    }
}
void afisare()
{
    for(int i = 0;i<rasp.size()-1;i++)
        g << rasp[i]<< " ";
}
int main()
{
    citire();
    if(verificare())
    {
        g << -1;
        return 0;
    }
    alg();
    afisare();

}