#include <bits/stdc++.h>
using namespace std;

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

int n, m;
vector<int> L[100005], euler;
int d[100005], X[500005], Y[500005], ind[100005], viz[500005];

bool Pare()
{
    for (int i = 1; i <= n; i++)
        if (d[i] % 2 == 1)return false;
    return true;
}
void Euler(int k)
{
    while (ind[k] < L[k].size())
    {
        int i = L[k][ind[k]];
        ind[k]++;
        if (viz[i] == 0)
        {
            viz[i] = 1;
            Euler(X[i] + Y[i] - k);
        }
    }
    euler.push_back(k);
}
int main()
{
    int i, j, p;
    fin >> n >> m;
    for (p = 1; p <= m; p++)
    {
        fin >> i >> j;
        d[i]++; d[j]++;
        X[p] = i; Y[p] = j;
        L[i].push_back(p);
        L[j].push_back(p);
    }

    if (Pare() == false)fout << -1 << "\n";
    else
    {
        Euler(1);
        euler.pop_back();
        for (int i : euler)
            fout << i << " ";
        fout << "\n";
    }

    return 0;
}