#include <fstream>
#include <iostream>
#include <stack>
#include <vector>
#define MUCHII 500005
using namespace std;

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

struct shape
{
    int x, y;
    bool ap = false;
} v[500005];


vector <int> g[100005];

stack <int> stiva;

int n, m;

void citire()
{
    in >> n >> m;

    for(int i = 1; i <= m; i++)
    {
       in >> v[i].x >> v[i].y;
       g[v[i].x].push_back(i);
       g[v[i].y].push_back(i);
    }
}

void parcurgere()
{
    stiva.push(1);

    while(!stiva.empty())
    {
        int nod = stiva.top();

        if(g[nod].size())
        {
            int next = g[nod].back();
            g[nod].pop_back();

            if(v[next].ap == true)
                continue;

            v[next].ap = true;

            if(v[next].x == nod)
                stiva.push(v[next].y);
            else
                stiva.push(v[next].x);
        }
        else
        {
            out << stiva.top() << " ";
            stiva.pop();
        }
    }
}

int main()
{
    citire();

    for(int i = 1; i <= n; i++)
        if(g[i].size() % 2 != 0)
        {
            out << "-1";
            return 0;
        }
    parcurgere();
    return 0;
}