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

bool citire(std::vector<std::vector<std::pair<int, int> > > &graf, int &n, int &m) {
    int i, j;
    int index = 1;
    std::ifstream f("ciclueuler.in");
    f >> n >> m;
    graf.resize(n + 1);
    std::vector<int> grad(n + 1);
    for (int k = 1; k <= m; ++k) {
        f >> i >> j;
        graf[i].emplace_back(j, index);
        graf[j].emplace_back(i, index);
        ++grad[i], ++grad[j], ++index;
    }
    f.close();

    // toate varfurile au grad par <=> graf eulerian
    for (i = 1; i <= n; ++i)
        if (grad[i] % 2 != 0)
            return false;
    return true;
}

void sol() {
    std::vector<std::vector<std::pair<int, int> > > graf;
    int n, m;
    if (!citire(graf, n, m)) {
        std::ofstream g("ciclueuler.out");
        g << -1;
        g.close();
        return;
    }

    std::vector<int> ciclu;
    std::stack<int> s;
    s.push(1);
    std::vector viz(m + 1, false);
    while (!s.empty()) {
        const int i = s.top();
        if (!graf[i].empty()) {
            const auto [j, index] = graf[i].back();
            graf[i].pop_back();
            if (!viz[index]) {
                viz[index] = true;
                s.push(j);
            }
        } else {
            s.pop();
            ciclu.push_back(i);
        }
    }

    std::ofstream g("ciclueuler.out");
    for (const auto &i: ciclu)
        g << i << " ";
    g.close();
}

int main() {
    sol();
    return 0;
}