#include <bits/stdc++.h>
using namespace std;

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

int n, m;
vector<vector<pair<int, int>>> ad;

vector<bool> vis;
vector<int> cycle;

void dfs(int node) {
    while (!ad[node].empty()) {
        auto back = ad[node].back();
        ad[node].pop_back();
        if (!vis[back.second]) {
            vis[back.second] = true;
            dfs(back.first);
        }
    }
    cycle.push_back(node);
}

int main() {
    fin >> n >> m;
    ad.resize(n + 1);
    for (int i = 0; i < m; i++) {
        int x, y; fin >> x >> y;
        ad[x].emplace_back(y, i);
        ad[y].emplace_back(x, i);
    }

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

    vis.resize(m);
    dfs(1);
    cycle.pop_back();

    for (int node : cycle)
        fout << node << ' ';
    fout << '\n';

    fout.close();
    return 0;
}