#include <fstream>
#include <algorithm>
#include <vector>
#include <stack>

using namespace std;

const int NMAX = 100000 + 5;
const int MMAX = 5 * NMAX;

struct Edge {
    int a, b;
    bool vis;

    int other(int node) {
        if (node == a)
            return b;
        else
            return a;
    }
} edges[MMAX];

int N, M;
vector <int> graph[NMAX];

stack <int> stk;
vector <int> sol;

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

    cin >> N >> M;
    for (int i = 1; i <= M; ++ i) {
        cin >> edges[i].a >> edges[i].b;

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

    bool bad = false;
    for (int i = 1; i <= N; ++ i)
        if (graph[i].size() % 2 == 1) {
            bad = true;
            break;
        }

    if (bad) {
        cout << "-1\n";
        return 0;
    }

    stk.push(1);
    while (!stk.empty()) {
        int node = stk.top();

        bool found = false;
        for (int i = 0; i < graph[node].size(); ++ i)
            if (!edges[graph[node][i]].vis) {
                edges[graph[node][i]].vis = true;
                stk.push(edges[graph[node][i]].other(node));
                found = true;
                break;
            }

        if (!found) {
            stk.pop();
            sol.push_back(node);
        }
    }

    reverse(sol.begin(), sol.end());
    sol.pop_back();
    for (int i = 0; i < sol.size(); ++ i)
        cout << sol[i] << " \n"[i + 1 == sol.size()];
    return 0;
}