#include <bits/stdc++.h>
using namespace std;
ifstream fin ("ciclueuler.in");
ofstream fout ("ciclueuler.out");
const int NMAX = 1e5 + 5;
const int MMAX = 5e5 + 5;
int a[MMAX], b[MMAX], viz[MMAX];
int n, m, ok;
vector<int> v[NMAX];
void citire()
{
    fin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        fin >> a[i] >> b[i];
        v[a[i]].push_back(i);
        v[b[i]].push_back(i);
    }
}
void euler(int nod)
{
    while (v[nod].size() != 0) {
        int muchia_curenta = v[nod].back();
        v[nod].pop_back();
        if (viz[muchia_curenta])
            continue;
        viz[muchia_curenta] = 1;
        int vefin = (nod ^ a[muchia_curenta] ^ b[muchia_curenta]);
        euler(vefin);

    }
    if (ok)
        fout << nod << " ";
    ok = 1;
}
int main()
{
    citire();
    bool pp = true;
    for (int i = 1; i <= n; i++)
        if (v[i].size() % 2 == 1)
            pp = false;
    if (pp == false)
        fout << -1;
    else
    {
        euler(1);
    }

    return 0;
}