#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
using VI  = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;
using VP  = vector<PII>;
using VB  = vector<bool>;
VVI g;
VI ciclu;
VB erased;
VP muchie;
vector<vector<int>::iterator> ramas;
int n, m;
inline void Euler(int const& start) {
    stack<int> stiva;
    stiva.emplace(start);
    while (!stiva.empty()) {
        int x = stiva.top(), to_push = 0;
        for (; ramas[x] != g[x].end(); ++ramas[x]) {
            int ind = *ramas[x];
            if (!erased[ind]) {
                erased[ind] = 1;
                int y = muchie[ind].first;
                if (x == y)
                    y = muchie[ind].second;
                to_push = y;
                break;
            }
        }
        if (!to_push) {
            stiva.pop();
            ciclu.emplace_back(x);
        }
        else stiva.emplace(to_push);
    }
}
int main() {
    fin >> n >> m;
    g = VVI(n + 1);
    muchie = VP(m + 1);
    for (int i = 1; i <= m; ++i) {
        int x, y;
        fin >> x >> y;
        muchie[i] = {x, y};
        g[x].emplace_back(i);
        g[y].emplace_back(i);
    }
    ramas.resize(n + 1);
    for (int i = 1; i <= n; ++i) {
        ramas[i] = g[i].begin();
        if (g[i].size() % 2) {
            fout << -1;
            return 0;
        }
    }
    erased = VB(m + 1);
    Euler(1);
    ciclu.pop_back();
    for (int const& x : ciclu)
        fout << x << ' ';
    fin.close();
    fout.close();
    return 0;
}