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

#define MAX 100010

using namespace std;

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

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

void dfs(int node)
{
    if (viz[node] == 1)
    {
        return;
    }
    viz[node] = 1;

    for (size_t i = 0; i < G[node].size(); ++i)
    {
        dfs(G[node][i]);
    }
}

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

        while (!G[node].empty())
        {
            int nnode = G[node][G[node].size() - 1];
            G[node].pop_back();
            for (size_t i = 0; i < G[nnode].size(); ++i)
            {
                if (G[nnode][i] == node)
                {
                    G[nnode][i] = G[nnode][G[nnode].size() - 1];
                    G[nnode].pop_back();
                    break;
                }
            }
            s.push(nnode);
            goto here;
        }
        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 = 0; i < n; ++i)
    {
        if (G[i].size() % 2 != 0)
        {
            eulerian = false;
        }
    }

    dfs(1);

    for (int i = 1; i <= n; ++i)
    {
        if (viz[i] == 0)
        {
            eulerian = false;
        }
    }

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

    return 0;
}