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

using namespace std;

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

const int nmax = 100000;

int n;
int grad[nmax + 2];
stack <int> st;
deque <int> dq;
vector <int> v[nmax + 2];
bool vizitat[nmax + 2];


void citeste () {
    int m;
    f >> n >> m;
    int a, b;
    for (int i = 1; i <= m; i++) {
        f >> a >> b;
        v[a].push_back (b);
        v[b].push_back (a);
        grad[a]++; grad[b]++;
    }
    //for (int i = 1; i <= n; i++) cout << grad[i] << ' ';
}

void DFS (int nod) {
    vizitat[nod] = true;
    int l = (int)v[nod].size ();
    for (int i = 0; i < l; i++)
        if (!vizitat[v[nod][i]]) DFS (v[nod][i]);
}

int OK () {
    for (int i = 1; i <= n; i++)
        if (!vizitat[i] || grad[i] % 2 == 1) return 0;
    return 1;
}

void euler () {
    st.push(1);
    int nod, x;
    while (!st.empty ()) {
        nod = st.top ();
        if (!v[nod].size ()) {
            g << nod << ' ';
            st.pop ();
        }
        else {
            x = v[nod].back ();
            st.push (x);
            v[x].erase (find(v[x].begin (), v[x].end (), nod));
            v[nod].pop_back ();
        }
    }
}


int main () {
    citeste ();
    DFS (1);
    if (OK ()) euler ();
    else g << -1;
    g << '\n';
    return 0;
}