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

struct Edge {
    int from, to;
    bool check;
};

bool valid(std::vector<std::list<int>> &graph, std::vector<Edge> &edges, int nV) {

    for (int i(1); i <= nV; i++) {
        if (graph[i].size() & 1) {
            return false;
        }
    }

    std::vector<bool> check(nV + 1, false);
    std::list<int> myQ;

    check[1] = true;
    myQ.push_back(1);

    int node;
    while (!myQ.empty()) {
        node = myQ.front();
        myQ.pop_front();
        for (int edge : graph[node]) {
            if (!check[edges[edge].from]) {
                check[edges[edge].from] = true;
                myQ.push_back(edges[edge].from);
            }
            if (!check[edges[edge].to]) {
                check[edges[edge].to] = true;
                myQ.push_back(edges[edge].to);
            }
        }
    }

    for (int i(1); i <= nV; i++) {
        if (!check[i]) {
            return false;
        }
    }

    return true;
}

void visit(std::vector<std::list<int>> &graph,
    std::vector<Edge> &edges, std::vector<int> &res) {

    std::stack<int> myStack;
    myStack.push(1);

    bool fin;

    while (!myStack.empty()) {
        fin = true;
        for (auto edge = graph[myStack.top()].begin(); edge != graph[myStack.top()].end(); edge++) {
            if (edges[*edge].check) {

                fin = false;

                edges[*edge].check = false;

                if (edges[*edge].from != myStack.top()) {
                    myStack.push(edges[*edge].from);
                } else {
                    myStack.push(edges[*edge].to);
                }

                break;
            }
        }
        if (fin) {
            res.push_back(myStack.top());
            myStack.pop();
        }
    }
}

int main() {
    std::ifstream fileIn("ciclueuler.in");
    std::ofstream fileOut("ciclueuler.out");

    int nV, nM;

    fileIn >> nV >> nM;

    std::vector<std::list<int>> graph(nV + 1);
    std::vector<Edge> edges(nM);

    int a, b;
    for (int i(0); i < nM; i++) {
        fileIn >> a >> b;

        edges[i].from = a;
        edges[i].to = b;
        edges[i].check = true;

        graph[a].push_back(i);
        graph[b].push_back(i);
    }

    std::vector<int> res;

    if (!valid(graph, edges, nV)) {
        fileOut << -1;
    } else {
        visit(graph, edges, res);
        for (auto node = res.begin(); node != res.end(); node++) {
            fileOut << *node << ' ';
        }
    }

    fileIn.close();
    fileOut.close();
    return 0;
}