#include <fstream>
#include <vector>
#include <queue>
#include <iostream>

using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

const int NMAX = 100005;
int n, m, was[NMAX], viz[5 * NMAX], Stack[5 * NMAX];
vector < pair < int, int > > v[NMAX];

void dfs(int node) {
    viz[node] = 1;
    for (auto it : v[node])
        if (!viz[it.first])
            dfs(it.first);
}

int main() {
    int i, x, y, root;
    f >> n >> m;
    for (i = 1; i <= m; i++) {
        f >> x >> y;
        v[x].push_back(make_pair(y, i));
        v[y].push_back(make_pair(x, i));
        was[x]++;
        was[y]++;
    }

    for (i = 1; i <= n; i++)
        if (was[i]) {
            dfs(i);
            root = i;
            i = n;
        }

    for (i = 1; i <= n; i++) {
        if (v[i].size() % 2 == 1 || (was[i] && !viz[i])) {
            g << -1;
            return 0;
        }
        viz[i] = 0;
    }

    int elem = 1, node, neighbour;
    deque < int > q;
    q.push_back(root);
    bool ok = 0;
    while (!q.empty()) {
        node = q.back();
        if (!was[node]) {
            if (ok) {
                g << node << " ";
                q.pop_back();
                continue;
            }
            else {
                ok = 1;
                q.pop_back();
                continue;
            }
        }

        while (!v[node].empty() && viz[v[node].back().second] == 1)
            v[node].pop_back();

        neighbour = v[node].back().first;
        was[node]--;
        was[neighbour]--;
        viz[v[node].back().second] = 1;
        v[node].pop_back();

        q.push_back(neighbour);
    }

    return 0;
}