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

int n, m;

vector<vector<pair<int, int> > > graph;
vector<int> cycle;
vector<bool> edge;

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

    fin>>n>>m;

    graph.resize(n+1, vector<pair<int, int> >());
    edge.resize(m+1, true);

    int x, y;
    for(auto i=1; i<=m; i++){
        fin>>x>>y;
        graph.at(x).push_back(make_pair(y, i));
        graph.at(y).push_back(make_pair(x, i));
    }

    for(size_t i=1; i<graph.size(); i++) if(graph.at(i).size()&1){

        fout<<-1;
        return 0;
    }

    stack<int> Stack;   Stack.push(1);

    while(!Stack.empty()){
        int current_node = Stack.top();

        if(!graph.at(current_node).empty()){
            int neighbour = graph.at(current_node).back().first;
            int Index = graph.at(current_node).back().second;

            graph.at(current_node).pop_back();

            if(edge.at(Index)==true){
                edge.at(Index) = false;
                Stack.push(neighbour);
            }

        } else {
            Stack.pop();
            cycle.push_back(current_node);
        }
    }

    cycle.pop_back();
    for(auto& elem:cycle) fout<<elem<<" ";
}