#include <fstream>
#include <vector>

using namespace std;

ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

struct Info {
    int node2;
    int id;
    Info() = default;
    Info(int node2, int id) : node2(node2), id(id) {}
};

int n, m;
vector<vector<Info>> graph;
vector<int> rs;

void read() {
    cin >> n >> m;
    graph.resize(n + 1);
    for (int i = 1; i <= m; i++) {
        int a, b;
        cin >> a >> b;
        graph[a].push_back(Info(b, i));
        graph[b].push_back(Info(a, i));
    }
}

void dfs(int node, bool *vis) {
    while (!graph[node].empty()) {
        if (vis[graph[node].back().id] == true) {
            graph[node].pop_back();
            continue;
        }

        vis[graph[node].back().id] = true;

        int temp = graph[node].back().node2;
        graph[node].pop_back();
        dfs(temp, vis);
    }
    rs.push_back(node);
}

void solve() {
    for (int i = 1; i <= n; i++) {
        if (graph[i].size() % 2) {
            cout << -1;
            return;
        }
    }

    bool *vis = new bool[m + 1];
    fill(vis, vis + m + 1, false);

    dfs(1, vis);
    rs.pop_back();

    for (auto it : rs) {
        cout << it << " ";
    }

    delete[] vis;
}

int main() {

    read();
    solve();
    return 0;
}