// Hierholzer's algorithm
#include <vector>
#include <list>
#include <array>
#include <algorithm>
#include <fstream>
#include <stack>
using namespace std;

const int nmax = 100005;

vector<int> graph[nmax];
array<int, nmax> visited;
vector<int> solution;
stack<int> st;
int n, m;
int found;

void read() {
    ifstream in("ciclueuler.in");
    int u, v;
    in >> n >> m;
    for (int i = 1; i <= m; ++i) {
        in >> u >> v;
        graph[u].push_back(v);
        graph[v].push_back(u);
    }
}

void dfs(int u) {
    visited[u] = 1;
    ++found;
    for (auto v : graph[u])
        if (!visited[v]) dfs(v);
}

void remove_edge(int u, int v) {
    graph[u].pop_back();
    for (auto it = graph[v].begin(); it != graph[v].end(); ++it)
        if (*it == u) {
            swap(*it, graph[v].back());
            graph[v].pop_back();
            return;
        }
}

bool is_euler() {
    for (int i = 1; i <= n; ++i)
        if (graph[i].size() % 2 != 0)
            return 0;
    dfs(1);
    if (found != n)
        return 0;
    return 1;
}

void euler_tour(int x) {
    st.push(x);
    while (!st.empty()) {
        int u = st.top();
        while (!graph[u].empty()) {
            int v = graph[u].back();
            remove_edge(u, v);
            st.push(v);
            u = v;
        }
        solution.push_back(u);
        st.pop();
    }
}

void write(bool is_good) {
    ofstream out("ciclueuler.out");
    if (!is_good) {
        out << "-1\n";
    }
    else {
        euler_tour(1);
        solution.pop_back();
        for (auto u : solution)
            out << u << ' ';
    }
}


int main() {
    read();
    write(is_euler());
    return 0;
}