#include <fstream>
#include <vector>
#include <stack>
#include <algorithm>

using namespace std;
ifstream in("ciclueuler.in"); ofstream out("ciclueuler.out");


vector <int> lista[100001];

bool ok[500001];

stack<int> st;

void euler(int nod) {
    int fiu;
    while (!lista[nod].empty()){
        st.push(nod);
        fiu = lista[nod].back();
        lista[nod].pop_back();

        for (auto it = lista[fiu].begin(); it != lista[fiu].end(); ++it) {
            if (*it == nod) {
                lista[fiu].erase(it);
                break;
            }
        }
        nod = fiu;
    }
}

int main() {
    int n, m, nod1, nod2;
    in >> n >> m;

    for (int i = 1; i <= m; i++) {
        in >> nod1 >> nod2;
        lista[nod1].push_back(nod2);
        lista[nod2].push_back(nod1);
    }

    bool possible = true;
    for (int i = 1; i <= n; i++) {
        if (lista[i].size() % 2 == 1) {
            possible = false;
            break;
        }
    }

    if (!possible) {
        out << "-1";
    } else {
        int nod = 1;
        bool finished = false;
        while (!st.empty() || !finished) {
            finished = true;
            out << nod << " ";
            euler(nod);
           // if (!st.empty()) { /// imi afiseaza si ultimul element (primul din nou)
            nod = st.top();
            st.pop();
                //finished = false;
            //}
        }
    }
    return 0;
}