#include <fstream>
#include <vector>
#include <stack>
#define NMAX 100002
using namespace std;
ifstream  fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int N,M,grad[NMAX],viz[NMAX],f[5*NMAX];
stack<int> stiva;
vector<int> sol;
vector<pair<int,int> > graph[NMAX];

void citire()
{
    fin>>N>>M;

    int u,v;
    for(int i=1; i<=M; i++)
    {
        fin>>u>>v;
        grad[u]++;
        grad[v]++;

        graph[u].push_back({v,i});
        graph[v].push_back({u,i});
    }
}

void DFS(int nod)
{
    viz[nod]=1;
    for(int i=0; i<graph[nod].size(); i++)
    {
        int next_nod=graph[nod][i].first;
        if(!viz[next_nod])
        {
            DFS(next_nod);
        }
    }
}

void euler(int start)
{
    stiva.push(start);

    while(!stiva.empty())
    {
        int nod=stiva.top();

        if(graph[nod].size()>0)
        {
            int next_nod=graph[nod].back().first;
            int muchie=graph[nod].back().second;
            graph[nod].pop_back();

            if(!f[muchie])
            {
                f[muchie]=1;
                stiva.push(next_nod);
            }
        }
        else
        {
            sol.push_back(nod);
            stiva.pop();
        }
    }
}

int main()
{
    citire();

    for(int i=1; i<=N; i++)
    {
        if(grad[i]%2==1)
        {
            fout<< -1 << "\n";
            return 0;
        }
    }

    euler(1);

    sol.pop_back();
    for(int i=0; i<sol.size(); i++)
    {
        fout<< sol[i] << " ";
    }
    fout<< "\n";

    return 0;
}