#include <bits/stdc++.h>
using namespace std;

int n, m;
vector<pair<int, int>> v[100001];
bool mt[500001];
stack<int> ans;

void euler() {
    stack<int> s;
    s.push(1);
    while (!s.empty()) {
        int node = s.top();
        if (!v[node].empty()) {
            pair<int, int> vn = v[node].back();
            v[node].pop_back();
            if (mt[vn.second] == 0) {
                mt[vn.second] = 1;
                s.push(vn.first);
            }
        } else {
            ans.push(node);
            s.pop();
        }
    }
}

int main() {
    ifstream cin("ciclueuler.in");
    ofstream cout("ciclueuler.out");
    cin >> n >> m;
    for (int i = 1; i <= m; ++i) {
        int x, y;
        cin >> x >> y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
    }
    for (int i = 1; i <= n; ++i) {
        if (v[i].size() % 2 != 0) {
            cout << -1;
            return 0;
        }
    }
    euler();
    while (ans.size() != 1) {
        cout << ans.top() << " ";
        ans.pop();
    }
}