#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;

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

const int NMAX = 100000;
int n, m;

struct muchie
{
    int x, y;
};

vector<int> G[NMAX+1], l;
vector<muchie> M;
vector<bool> elim;
stack<int> s;

void citire()
{
    int x, y;
    fin>>n>>m;
    while(m--)
    {
        fin>>x>>y;
        M.push_back({x, y});
        elim.push_back(0);
        G[x].push_back(M.size()-1);
        G[y].push_back(M.size()-1);
    }
}

void euler()
{
    s.push(1);
    while(!s.empty())
    {
        int v=s.top();
        if(G[v].size()>0)
        {
            int x=G[v].back();
            G[v].pop_back();
            if(!elim[x])
            {
                elim[x]=1;
                int p=M[x].y;
                if(p==v)
                    p=M[x].x;
                s.push(p);
            }
        }
        else
        {
            l.push_back(v);
            s.pop();
        }
    }
}

bool verif()
{
    for (int i=1; i<=n; i++)
        if(G[i].size()%2!=0)
            return 0;
    return 1;
}

int main()
{
    int x, y;
    fin>>n>>m;
    for (int i=1; i<=m; i++)
    {
        fin>>x>>y;
        M.push_back({x,y});
        elim.push_back(0);
        G[x].push_back(M.size()-1);
        G[y].push_back(M.size()-1);
    }

    if(!verif())
        fout<<"-1";
    else
    {
        euler();
        for (unsigned i=0; i<l.size()-1; i++)
            fout<<l[i]<<' ';
    }

    fin.close();
    fout.close();
    return 0;
}