#include <bits/stdc++.h>

using namespace std;

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

vector <int> L[500005];
int n, m, X[500005], Y[500005], P[500005], q[500005], k;
bool viz[500005];

void Citire()
{
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        fin >> X[i] >> Y[i];
        L[X[i]].push_back(i);
        L[Y[i]].push_back(i);
    }
}

inline bool Eulerian()
{
    for(int i = 1; i <= n; i++)
        if(L[i].size() % 2 == 1)
            return 0;
    return 1;
}

void DFS(int nod)
{
    while(P[nod] < L[nod].size())
    {
        int i = L[nod][P[nod]++];
        if(viz[i] == false)
        {
            viz[i] = true;
            DFS(X[i] + Y[i] - nod);
        }
    }
    q[++k] = nod;
}

void Rezolvare()
{
    DFS(X[1]);
    for(int i = 1; i < k; i++)
        fout << q[i] << " ";
    fout << "\n";
}

void Verificare()
{
    if(Eulerian()) Rezolvare();
    else fout << "-1\n";
}

int main()
{
    Citire();
    Verificare();
    return 0;
}