#include <bits/stdc++.h>
#define pf push_front
#define pb push_back

using namespace std;

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

const int NMax = 100005;

vector <int> :: iterator it;
vector <int> G[NMax];
list <int> Q;

int n, m, x, y;

int main()
{
    f >> n >> m;

    for (int i = 1; i <= m; i++)
    {
        f >> x >> y;
        G[x].pb(y);
        G[y].pb(x);
    }

    for (int i = 1; i <= n; i++)
    {
        if (G[i].size() % 2 == 1)
        {
            g << -1;
            return 0;
        }
    }

    Q.pb(1);
    while (!Q.empty())
    {
        x = Q.front();
        if (G[x].size() == 0)
        {
            if (Q.size() == 1) break;

            g << x << " ";
            Q.pop_front();

            continue;
        }
        else
        {
            int aux = G[x].back();
            Q.pf(aux);
            G[x].pop_back();
            for (it = G[aux].begin(); it != G[aux].end(); it++)
            {
                if (*it == x)
                {
                    G[aux].erase(it);
                    break;
                }
            }
        }
    }
    return 0;
}