#include <fstream>
#include <vector>
#define mp make_pair
#define edge g[nod][g[nod].size() - 1]
using namespace std;

ifstream is("ciclueuler.in");
ofstream os("ciclueuler.out");

using II = pair<int, int>;
using VI = vector<int>;
using VII = vector<II>;
using VVI = vector<vector<int>>;

int n, m;
VVI g;
VII e;
VI answ, viz;

void Read();
bool Check();
void Euler(int nod);

int main()
{
    Read();
    if ( !Check )
        os << "-1\n";
    else
    {
        viz = VI(m);
        Euler(1);
    }
    is.close();
    os.close();
    return 0;
}

inline void Euler(int nod)
{
    while ( g[nod].size() )
        if ( viz[edge] )
            g[nod].pop_back();
        else
        {
            viz[edge] = 1;
            Euler(e[edge].first + e[edge].second - nod);
        }
    if ( answ.size() )
    {
        os << answ[0] << " ";
        answ.pop_back();
    }
    answ.push_back(nod);
}

bool Check()
{
    for ( int i = 1; i <= n; ++i )
        if ( g[i].size() & 1 )
            return false;
    return true;
}

void Read()
{
    is >> n >> m;
    g = VVI(n + 1);
    int n1, n2;
    for ( int i = 0; i < m; ++i )
    {
        is >> n1 >> n2;
        g[n1].push_back(i);
        g[n2].push_back(i);
        e.push_back(mp(n1, n2));
    }
}