#include <fstream>
#include <vector>
#include <stack>

using namespace std;

ifstream fin ("ciclueuler.in");
ofstream fout ("ciclueuler.out");

const int NMAX = 100010;
const int MMAX = 500010;

struct muchie {int u, v; bool del;} m[MMAX];

int N, M;
vector<int> g[NMAX];
stack<int> st, ANS;

int main () {
    fin >> N >> M;
    for (int i = 1; i <= M; i++) {
        fin >> m[i].u >> m[i].v;
        g[m[i].u].push_back (i);
        g[m[i].v].push_back (i);
    }

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

    st.push (1);
    while ( !st.empty ()) {
        int nod = st.top();

        if ( !g[nod].empty ()) {
            int i = g[nod].back ();
            g[nod].pop_back ();

            if ( !m[i].del) {
                m[i].del = 1;
                if (m[i].v == nod) {
                    st.push (m[i].u);
                }
                else {
                    st.push (m[i].v);
                }
            }
        }
        else {
            ANS.push (nod);
            st.pop ();
        }
    }

    ANS.pop ();
    while ( !ANS.empty ()) {
        fout << ANS.top() << " ";
        ANS.pop();
    }

    fout << '\n';

    return 0;
}