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

#define NMAX 100005
#define MMAX 500005

using namespace std;

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

int N, M;

vector<vector<pair<int, int>>> gr;

bool used[MMAX];


void read() {
    fin >> N >> M;
    gr.resize(N + 1);
    int x, y;
    for (int i = 0; i < M; ++i)  {
        fin >> x >> y;
        gr[x].emplace_back(y, i);
        gr[y].emplace_back(x, i);
    }
}

bool isEuler() {
    for (int i = 1; i <= N; ++i) {
        if (gr[i].size() % 2 == 1) {
            return false;
        }
    }
    return true;
}

void euler(int nod) {
    stack<int> st;
    vector<int> answer;
    st.push(nod);
    while (!st.empty()) {

        int top = st.top();

        pair<int, int> edge = make_pair(-1, -1);
        for (int i = 0; i < gr[top].size(); ++i) {
            pair<int, int> v = gr[top][i];
            if (!used[v.second]) {
                edge = v;
                i = gr[top].size();
            }
        }

        if (edge.first == -1 && edge.second == -1) {
            answer.push_back(top);
            st.pop();
        }
        else {
            st.push(edge.first);
            used[edge.second] = true;
        }
    }

    for (int i = answer.size() - 1; i >= 1; --i) {
        fout << answer[i] << " ";
    }
    fout << "\n";
}

int main()
{
    read();
    if (!isEuler()) {
        fout << -1 << "\n";
    }
    else {
        euler(1);
    }
    return 0;
}