#include <iostream>
#include <algorithm>
#include <fstream>
#include <stack>
#include <vector>
#include <bitset>
using namespace std;

const int N = 1e5 + 1;

vector <pair<int, int> > L[N];
bitset <5 * N> vis;
vector <int> sol;
int n;

void Read ()
{
    ifstream fin ("ciclueuler.in");
    int m;
    fin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        L[x].push_back({y, i});
        L[y].push_back({x, i});
    }
    fin.close();
}

void CicluEulerian (int nod)
{
    stack <int> st;
    st.push(1);
    while (!st.empty())
    {
        int nod = st.top();
        if (L[nod].size()) {
            pair <int, int> next = L[nod].back();
            L[nod].pop_back();
            if (!vis[next.second])
            {
                vis[next.second] = 1;
                st.push(next.first);
            }
        }
        else
        {
            st.pop();
            sol.push_back(nod);
        }
    }
}

void Solve()
{
    ofstream fout ("ciclueuler.out");
    for (int i = 1; i <= n; i++)
        if (L[i].size() % 2 == 1)
        {
            fout << "-1\n";
            return;
        }
    CicluEulerian(1);
    for (int i = 0; i < sol.size() - 1; i++)
        fout << sol[i] << " ";
}

int main()
{
    Read();
    Solve();
    return 0;
}