#include <stdio.h>
#include <iostream>
#include <fstream>
#include <vector>
#include <array>
#include <algorithm>
#include <vector>
#include <stack>
#include <set>
#include <assert.h>
#include <queue>
#include <chrono>
#include <memory>
#include <cstring>

using LL = long long;
using ULL = int long long;

const std::string _problemName = "eulerian";

#define USE_FILES

#ifdef USE_FILES

namespace std {
std::ifstream fin(_problemName + ".in");
std::ofstream fout(_problemName + ".out");
}

#define cin fin
#define cout fout
#endif

using Edge = int;
using Graph = std::vector< std::vector<Edge> >;

bool hasEulerianCycle(const Graph& graph) {
    for (const auto& nodeNeighbours : graph) {
        if (nodeNeighbours.size() % 2 != 0) {
            return false;
        }
    }
    return true;
}

void addEdge(Graph& graph, int x, int y) {
    graph[x].push_back(y);
    graph[y].push_back(x);
}

std::vector<int> eulerianCycle;
Graph graph;

bool exists(const Edge& edge) {
    return edge != -1;
}

int getNeighbour(const Edge& edge) {
    return edge;
}

void remove(const Edge& edge) {

}

void dfs(int node) {
    bool hasNeighbour = false;
    for (auto& edge : graph[node]) {
        if (exists(edge)) {
            int neighbour = getNeighbour(edge);
            
            edge = -1;
            graph[neighbour]
            auto it = std::find(graph[neighbour].begin(), graph[neighbour].end(), node);
            *it = -1;

            dfs(neighbour);

            hasNeighbour = true;
            eulerianCycle.push_back(node);
        }
    }
    if (!hasNeighbour) {
        eulerianCycle.push_back(node);
    }
}

std::vector<int> buildEulerianCycle() {
    dfs(0);
}

int main() {

    int n, m;
    std::cin >> n >> m;

    graph.resize(n);

    while (m--) {
        int x, y;
        std::cin >> x >> y;
        --x, --y;
        addEdge(graph, x, y);
    }

    if (!hasEulerianCycle(graph)) {
        std::cout << "-1\n";
        return 0;
    }

    std::vector<int> eulerianCycle = buildEulerianCycle(graph);
    
    for (const auto node : eulerianCycle) {
        std::cout << node - 1 << ' ';
    }
    std::cout << '\n';

    return 0;
}