#include <fstream>
#include <iostream>
#include <vector>
#include <stack>
using namespace std;
vector <int> degrees;
vector <bool> processed;
///v[4] = [(5, 1), (6, 2)] -> muchie 4, 5 cu indicele 1, etc
vector< vector <pair <int, int> > > adj;
stack <int> path;
void initializeVectors(int numberOfNodes, int numberOfEdges) {
    degrees.resize(numberOfNodes + 1, 0);
    processed.resize(numberOfEdges + 1, false);
    adj.resize(numberOfNodes + 1);
}

bool hasEulerianCycle(int n) {
    for(int i = 1; i <= n; ++i) {
        if(degrees[i] % 2 != 0) {
            return false;
        }
        //cout << "yes";
    }
    return true;
}

void eulerian(int startNode) {

    for(unsigned int i = 0; i < adj[startNode].size(); ++i) {
        //cout << startNode << " " << i << "\n";
        int dest = adj[startNode][i].first;
        int edgeIndex = adj[startNode][i].second;
        if(!processed[edgeIndex]) {
            processed[edgeIndex] = true;
            eulerian(dest);
        }
    }
    path.push(startNode);
}


int main()
{
    ifstream f("ciclueuler.in");
    ofstream g("ciclueuler.out");
    int numberOfNodes, numberOfEdges;
    f >> numberOfNodes >> numberOfEdges;
    initializeVectors(numberOfNodes, numberOfEdges);
    for(int i = 1; i <= numberOfEdges; ++i){
        int src, dest;
        f >> src >> dest;
        adj[src].push_back(make_pair(dest, i));
        adj[dest].push_back(make_pair(src, i));
        degrees[src]++;
        degrees[dest]++;
    }
    if(hasEulerianCycle(numberOfNodes)){
        eulerian(1);
        while(path.size() > 1) {
            g << path.top() << " ";
            path.pop();
        }
    } else {
        g << -1;
    }
    f.close();
    g.close();
    return 0;
}