#include <fstream>
#include <vector>
using namespace std;

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

int n, m;
bool grd[100001], b[100001], M[100001], viz[100001];
vector<pair<int, int> > adj[100001];

void dfs(int nod)
{
    b[nod] = 1;
    for (int i = 0; i < adj[nod].size(); i++)
        if (!b[adj[nod][i].first])
        {
            M[adj[nod][i].second] = 1;
            dfs(adj[nod][i].first);
        }
}

void euler(int nod)
{
    while (adj[nod].size())
    {
        fout << nod << ' ';
        bool ok = true;
        for (int i = 0; i < adj[nod].size() && ok; i++)
        {
            int next = adj[nod][i].first, ind = adj[nod][i].second;
            if (!viz[ind] && !M[ind])
            {
                viz[ind] = 1;
                nod = next;
                ok = false;
            }
        }
        while (adj[nod].size() && ok)
        {
            int next = adj[nod].back().first, ind = adj[nod].back().second;
            adj[nod].pop_back();
            if (!viz[ind])
            {
                viz[ind] = 1;
                nod = next;
                ok = false;
            }
        }
    }
}

int main()
{
    int x, y;

    fin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        fin >> x >> y;
        adj[x].push_back(make_pair(y, i));
        if (x != y)
            adj[y].push_back(make_pair(x, i));
        grd[x] = !grd[x];
        grd[y] = !grd[y];
    }

    for (int i = 1; i <= n; i++)
        if (grd[i])
        {
            fout << -1;
            return 0;
        }

    dfs(1);
    euler(1);

    return 0;
}