#include <fstream>
#include <vector>
#include <bitset>

using namespace std;

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

int n, m;
vector<vector<pair<int, int>>> graf;
vector<int> grad, ciclu;
bitset<500005> viz;

void cauta_euler(int node) {
    while (graf[node].size() > 0) {
        int vecin = graf[node].back().first;
        int muchie = graf[node].back().second;
        graf[node].pop_back();
        if (!viz[muchie]) {
            viz[muchie] = 1;
            cauta_euler(vecin);
        }
    }
    ciclu.push_back(node);
}

int main() {
    cin >> n >> m;
    graf.assign(n + 2, vector<pair<int, int>>());
    grad.assign(n + 2, 0);
    for (int i = 1 ; i <= m ; ++i) {
        int src, dest;
        cin >> src >> dest;
        grad[src]++; grad[dest]++;
        graf[src].push_back({dest, i});
        graf[dest].push_back({src, i});
    }
    for (int i = 1 ; i <= n ; ++i) {
        if (grad[i] % 2 == 1) {
            cout << -1;
            return 0;
        }
    }
    cauta_euler(1);
    for (int i = 0 ; i < ciclu.size() - 1 ; ++i) {
        cout << ciclu[i] << " ";
    }
    return 0;
}