#include <iostream>
#include <fstream>
#include <vector>
#include <deque>
using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

vector<pair<int,int>> v[500003];
int n, m;
int x, y;
bool vizitat[500003];
deque<int> dq, ans;

void solve() {
    dq.push_back(1);
    while (!dq.empty()) {
        x = dq.back();
        while (!v[x].empty() && vizitat[v[x].back().first]) {
            v[x].pop_back();
        }
        if (v[x].empty()) {
            dq.pop_back();
            ans.push_back(x);
        } else {
            vizitat[v[x].back().first] = true;
            dq.push_back(v[x].back().second);
            v[x].pop_back();
        }
    }
}

int main() {
    fin >> n >> m;

    for (int i = 1; i <= m; ++i) {
        fin >> x >> y;
        v[x].push_back({i, y});
        v[y].push_back({i, x});
    }
    for (int i = 1; i <= n; ++i) {
        if (v[i].size() % 2 == 1) { ///fiecare nod are un nr par de vecini? (necesar pt a avea ciclu euler)
            fout << -1 << '\n';
            return 0;
        }
    }
    solve();
    ans.pop_back();
    while (!ans.empty()) {
        fout << ans.front() << ' ';
        ans.pop_front();
    }

    return 0;
}