#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

struct point
{
    int x, y;
};
int n, m;
vector <point> v[100003];
vector <int> rez;
int gr[100003];
stack <int> q;
bool folosit[500003];

void ciclueuler()
{
    q.push(1);
    while (!q.empty())
    {
        int x=q.top();
        if (gr[x]!=0)
        {
            if (folosit[v[x][gr[x]-1].y]==0)
            {
                folosit[v[x][gr[x]-1].y]=1;
                q.push(v[x][gr[x]-1].x);
            }
            gr[x]--;
        }
        else
        {
            q.pop();
            rez.push_back(x);
        }
    }
    for (int i=0; i<rez.size()-1; i++)
    {
        fout<<rez[i]<<" ";
    }
}

int main()
{
    int x, y;
    fin>>n>>m;
    for (int i=1; i<=m; i++)
    {
        fin>>x>>y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
        gr[x]++;
        gr[y]++;
    }
    for (int i=1; i<=n; i++)
    {
        if (gr[i]%2==1)
        {
            fout<<-1;
            return 0;
        }
    }
    ciclueuler();



    return 0;
}