#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <stack>
using namespace std;

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

const int NMAX = 100000 + 5;
const int MMAX = 500000 + 5;

queue <int> ans;
vector <int> graph[MMAX];
int n, m;
int st[MMAX], dr[MMAX];
bool vis[MMAX];
bool vis2[MMAX];

void read()
{
    fin >> n >> m;
    for (int i = 1; i <= m; ++i)
    {
        fin >> st[i] >> dr[i];
        graph[st[i]].push_back(i);
        graph[dr[i]].push_back(i);
    }
}

void dfs()
{
    stack<int>aux;
    aux.push(1);
    while (!aux.empty()){
        int nod = aux.top();
        vis2[nod] = true;

        //eliminate bad edges
        while (graph[nod].size() && vis[graph[nod].back()] == 1)
            graph[nod].pop_back();

        if (graph[nod].size())
        {
            int i = graph[nod].back();
            //cout << nod << " " << i << "\n";
            vis[i] = 1;
            graph[nod].pop_back();
            aux.push(st[i] + dr[i] - nod);
        }
        else
        {
            ans.push(nod);
            aux.pop();
        }
    }
}

bool check()
{
    for (int i = 1; i <= m; ++i)
        if (!vis[i])
            return 0;

    for (int i = 1; i <= n; ++i)
        if (!vis2[i])
            return 0;

    return 1;
}

void write()
{
    ans.pop();
    while (!ans.empty())
    {
        fout << ans.front() << " ";
        ans.pop();
    }
}

bool euler()
{
    for (int i = 1; i <= n; ++i)
        if (graph[i].size() % 2)
            return 0;
    return 1;
}

int main()
{
    read();
    if (euler())
        dfs();
    else
    {
        fout << -1;
        return 0;
    }

    if (check())
        write();
    else
        fout << -1;

    return 0;
}