#include <bits/stdc++.h>

using namespace std;

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

vector <int> L[100005];
int n, m, X[500005], Y[500005], q[500005], k;
int P[100001], viz[100001];

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])
        {
            viz[i] = 1;
            DFS(X[i] + Y[i] - nod);
        }
    }

    q[++k] = nod;
}

int main()
{
    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);
    }
    fin.close();

    if(Eulerian())
    {
        DFS(1);
        for(int i = 1; i < k; i++)
            fout << q[i] << " ";
    }
    else fout << "-1\n";

    fout.close();

    return 0;
}