#include <iostream>
#include <fstream>
#include <vector>
#include <queue>

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(int nod)
{
    vis2[nod] = true;

    for (int i = 0; i < graph[nod].size(); ++i)
    {
        if (!vis[graph[nod][i]])
        {
            vis[graph[nod][i]] = true;
            dfs(st[graph[nod][i]] + dr[graph[nod][i]] - nod);
        }
    }

    ans.push(nod);
}

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(1);
    else
    {
        fout << -1;
        return 0;
    }

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

    return 0;
}