#include <bits/stdc++.h>

using namespace std;

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

vector<int> G[100001];
vector<int> ans;
vector<int> cnt;

bool folosit[500001];
pair<int, int> muchie[500001];
int n, m;

void citire()
{
    fin >> n >> m;
    cnt.resize(n+1, 0);
    for (int i = 0; i < m; i++)
    {
        int x, y;
        fin >> x >> y;
        cnt[x]++, cnt[y]++;
        muchie[i].first = x;
        muchie[i].second = y;
    }

    for(int i = 1; i <= n; i++)
    {
        G[i].resize(cnt[i]);
        cnt[i] = 0;
    }

    for (int i = 0; i < m; i++)
    {
        int x = muchie[i].first;
        int y = muchie[i].second;
        G[x][cnt[x]++] = i;
        G[y][cnt[y]++] = i;
    }
}

void afisare()
{
    for (int i = 0; i < m; i++)
        fout << ans[i] << ' ';
}

void euler()
{
    ans.resize(m+1);
    int ansi = 0;
    int sti = 0;
    vector<int> st(m+1);
    st[sti++] = 1;
    while (sti)
    {
        int node = st[sti-1];
        if(cnt[node])
        {
            int e = G[node][--cnt[node]];
            if (!folosit[e])
            {
                folosit[e] = true;
                int rez = muchie[e].first ^ muchie[e].second ^ node;
                st[sti++] = rez;
            }
        }
        else
        {
            sti--;
            ans[ansi++] = node;
        }
    }
}

int main()
{
    citire();
    for (int i = 1; i <= n; i++)
        if (cnt[i] & 1)
        {
            fout << "-1\n";
            return 0;
        }

    euler();
    afisare();

    fin.close();
    fout.close();
}