#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <cassert>

#define Max 100005
 
using namespace std;
 
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
 
int N, M;
vector < pair<int,int> > edges[Max];

class Graph{
private:
    int NumberOfNodes, NumberOfEdges;
    vector<int> adjacencyList[Max];
 
public:
    Graph(int N, int M); // constructor

    void Euler(int k, int &ct, vector <int>&solutions, int visited[5*Max]);
    void Eulerian_Cycle();
};
 
// constructor
Graph :: Graph(int N, int M)
{
    NumberOfNodes = N;
    NumberOfEdges = M;
}
 
void Graph :: Euler(int k, int &ct, vector <int>&solutions, int visited[5*Max])
{
    while( !edges[k].empty() )
    {
        //x = indicele muchiei 
        //M[x].first = k
        //M[x].second = cealalta extremitate
        int edge = edges[k].back().first;
        int next = edges[k].back().second;
        if( visited[edge] == 0 )
        {
            visited[edge] = 1;
            Euler(next, ct, solutions, visited);
        }
    }
    ct++;
    solutions.push_back(k);
}
 
void Graph :: Eulerian_Cycle ()
{
    int x, y, i = 1;

    while ( fin >> x >> y )
    {
        edges[x].push_back({i, y});
        edges[y].push_back({i, x});
        i++;
    }
    
    for ( int i = 1; i <= NumberOfNodes; i++ )
        if ( edges[i].size() % 2 )
        {
            fout << "-1";
            return;
        }
    
    int visited[5*Max] = {0};
    int ct = 0;
    vector<int> solutions;

    Euler(1, ct, solutions, visited);

    solutions.pop_back();
    for ( auto i : solutions )
        fout << i << " ";
}

int main()
{
    fin >> N >> M;
    Graph G(N, M);
    G.Eulerian_Cycle();
    return 0;
}