#include <bits/stdc++.h>

using namespace std;

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

int n, m, len;
int sol[500003];
int st[500003], dr[500003];
bitset<500003> viz;
vector<int> h[500003];
unsigned int poz[500003];

void Citire()
{
    fin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        fin >> st[i] >> dr[i];
        h[st[i]].push_back(i);
        h[dr[i]].push_back(i);
    }
}

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


void Euler(int k)
{
    int i;
    while (poz[k] < h[k].size())
    {
        i = h[k][poz[k]];
        poz[k]++;
        if (viz[i] == 0)
        {
            viz[i] = 1;
            ///if (k == st[i]) Euler(dr[i]);
            ///else Euler(st[i]);
            Euler(st[i] + dr[i] - k);
        }
    }
    sol[++len] = k;
}

int main()
{
    Citire();
    if (Pare() == 0) fout << "-1\n";
    else
    {
        Euler(1);
        for (int i = 1; i <= len; i++)
            fout << sol[i] << " ";
    }
    return 0;
}