#include <fstream>
#include <list>
#include <queue>
#include <stack>

using namespace std;

const int MAXN = 100002;

int n, m;
bool vis[MAXN];
list<int> g[MAXN];
queue<int> q;
stack<int> s;
ofstream out("ciclueuler.out");
int counter = 0;

void bfs()
{
    q.push(1);
    vis[1] = 1;
    int x;
    while(!q.empty())
    {
        x = q.front();
        q.pop();
        for (list<int>::iterator it = g[x].begin(); it != g[x].end(); it++)
            if (!vis[*it])
            {
                vis[*it] = 1;
                q.push(*it);
            }
    }
}

void deleteEdge(int v, int w)
{
    for (list<int>::iterator it = g[w].begin(); it != g[w].end(); it++)
        if (*it == v)
        {
            it = g[w].erase(it);
            break;
        }
}

void euler(int x)
{
    s.push(x);
    int v, w;
    while (!s.empty())
    {
        v = s.top();
        if (g[v].empty())
        {
            ++counter;
            if (counter <= m)
                out << v << ' ';
            s.pop();
        }
        else
        {
            w = g[v].front();
            g[v].pop_front();
            deleteEdge(v, w);
            s.push(w);
        }
    }
}

int main()
{
    ifstream in("ciclueuler.in");

    in >> n >> m;
    for (int x, y, i = 1; i <= m; i++)
    {
        in >> x >> y;
        g[x].push_back(y);
        g[y].push_back(x);
    }

    bfs();

    bool conex = true;
    for (int i = 1; i <= n; i++)
        if (!vis[i])
        {
            conex = false;
            break;
        }

    bool eulerian = true;
    for (int i = 1; i <= n; i++)
        if (g[i].size() % 2 == 1)
        {
            eulerian = false;
            break;
        }
    if (conex == false || eulerian == false)
    {
        out << "-1\n";
        return 0;
    }

    euler(1);
    out << '\n';

    return 0;
}