#include <bits/stdc++.h>

using namespace std;

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];
//vector<int> ans;

void citire() {
    cin >> n >> m;
    for (int i = 1; i <= m; i++) {
        cin >> 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 vecin = (nod ^ a[muchia_curenta] ^ b[muchia_curenta]);
        /*int vecin;
        if (a[muchia_curenta] == nod)
            vecin = b[muchia_curenta];
        else
            vecin = a[muchia_curenta];*/
        euler(vecin);

    }
    if (ok)
        cout << nod << " ";
    ok = 1;
    //ans.push_back(nod);
}

int main() {

    freopen ("ciclueuler.in", "r", stdin);
    freopen ("ciclueuler.out", "w", stdout);

    citire();
    bool pp = true;
    for (int i = 1; i <= n; i++)
        if (v[i].size() % 2 == 1)
            pp = false;

    if (pp == false)
        cout << -1;
    else {
        euler(1);
      //  for (int i = 0; i < ans.size() - 1; i++)
        //    cout << ans[i] << " ";
    }


    return 0;
}