#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <algorithm>

#define MAX 100010

using namespace std;

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

vector<int> G[MAX];
vector<int> sol;
stack<int> s;

void euler(int node_arg)
{
    s.push(node_arg);
    while (!s.empty())
    {
        int node = s.top();

        if (!G[node].empty())
        {
            int nnode = G[node][0];
            G[node].erase(G[node].begin());
            G[nnode].erase(find(G[nnode].begin(), G[nnode].end(), node));
            s.push(nnode);
            continue;
        }
        sol.push_back(node);

        s.pop();
    }
}

int main()
{
    int n, m;
    f >> n >> m;
    for (int i = 0; i < m; ++i)
    {
        int x, y;
        f >> x >> y;
        G[x].push_back(y);
        G[y].push_back(x);
    }

    bool eulerian = true;
    for (int i = 1; i <= n; ++i)
    {
        if (G[i].size() % 2 != 0)
        {
            eulerian = false;
        }
    }

    if (eulerian)
    {
        euler(1);
        if (sol.size() - 1 == m)
        {
            for (int i = 0; i < sol.size() - 1; ++i)
            {
                cout << sol[i] << ' ';
            }
        }
        else
        {
            cout << -1 << '\n';
        }
    }
    else
    {
        cout << -1 << '\n';
    }

    return 0;
}