#include <bits/stdc++.h>

using namespace std;

const int NMAX = 100002;

vector < pair < int , int > > v[NMAX];
vector < int > sol;
queue < int > q;
bitset < NMAX > mark, del;
stack < int > st;

int nr[NMAX];
int n, m;

void bfs(int st)
{
    mark[st] = 1;
    q.push(st);
    while(!q.empty())
    {
        int nod = q.front();
        q.pop();

        for(int i = 0; i < v[nod].size(); i++)
            if(!mark[v[nod][i].first])
                mark[v[nod][i].first] = 1, q.push(v[nod][i].first);
    }
}

bool isEuler()
{
    bfs(1);
    for(int i = 1; i <= n; i++)
        if(!mark[i] || v[i].size() % 2)
            return 0;
    return 1;
}

int main()
{
    ifstream f("ciclueuler.in");
    ofstream g("ciclueuler.out");
    f >> n >> m;
    for(int i = 1, x, y; i <= m; i++)
    {
        f >> x >> y;
        v[x].push_back({y, i});
        v[y].push_back({x, i});
    }

    if(isEuler())
    {
        for(int i = 1; i <= n; i++)
            nr[i] = v[i].size();

        st.push(1);
        while(!st.empty())
        {
            int x = st.top();
            if(v[x].size())
            {
                int y = v[x][v[x].size() - 1].first, ind = v[x][v[x].size() - 1].second;
                if(!del[ind])
                {
                    del[ind] = 1;
                    st.push(y);
                }
                v[x].pop_back();
            }
            else
            {
                sol.push_back(x);
                st.pop();
            }

        }
        for(int i = 0; i < sol.size() - 1; i++)
            g << sol[i] << " ";
    }
    else
        g << -1;

    g << '\n';
    f.close();
    g.close();
    return 0;
}