//#include <iostream>
#include <fstream>
#include <vector>

// cu Fleury flurry
using namespace std;

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

const int N=100005;
const int M=500005;

int n, m, viz[M];
vector <pair <int, int> > a[N];
vector <int> q, v;

void dfs(int i)
{
    int u;
    q.push_back(i);
    while (!q.empty())
    {
        u=q.back();
        if (!a[u].empty())
        {
            pair <int , int> w;
            w=a[u].back();
            a[u].pop_back();
            if (!viz[w.second])
            {
                viz[w.second]=1;
                q.push_back(w.first);
            }
        }
        else
        {
            q.pop_back();
            v.push_back(u);
        }
    }
}
int main()
{
    int i, x, y;

    f>>n>>m;
    for (i=1; i<=m; i++)
    {
        f>>x>>y;
        a[x].push_back(make_pair(y, i));
        a[y].push_back(make_pair(x, i));
    }

    // verific daca are gradul par
    for (i=1; i<=n; i++)
      if (a[i].size() % 2 == 1) { cout<<-1; return 0; }

    dfs(1);

    for (i=0; i<v.size()-1; i++) cout<<v[i]<<" ";
    return 0;
}