#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);
    }
}

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

void DFS(int x)
{
    while(P[x] <L[x].size())
    {
        int i = L[x][P[x]++];

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

    q[++k] = x;
}

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

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