#include <fstream>
#include <vector>
using namespace std;
ifstream cin ("ciclueuler.in");
ofstream cout ("ciclueuler.out");
vector<pair<int,int> > g[100005];
vector<int> rasp;
int d[100005];
bool u[100005];
bool muchii[500005];
void dfs(int nod)
{
    u[nod] = true;
    for(auto urm:g[nod])
    {
        if(u[urm.first])
            continue;
        dfs(urm.first);
    }
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n,m;
    cin >> n >> m;
    for(int i=1;i<=m;i++)
    {
        int a,b;
        cin >> a >> b;
        g[a].push_back({b,i});
        g[b].push_back({a,i});
        d[a]++;
        d[b]++;
    }
    for(int i=1;i<=n;i++)
    {
        if(d[i]%2!=0)
        {
            cout << "-1" << '\n';
            return 0;
        }
    }
    dfs(1);
    for(int i=1;i<=n;i++)
    {
        if(u[i])
            continue;
        cout << "-1";
        return 0;
    }
    vector<int> st;
    st.push_back(1);
    while(!st.empty())
    {
        int vf = st.back();
        if(g[vf].empty())
        {
            st.pop_back();
            rasp.push_back(vf);
            continue;
        }
        pair<int,int> muchie = g[vf].back();
        g[vf].pop_back();
        if(muchii[muchie.second])
            continue;
        st.push_back(muchie.first);
        muchii[muchie.second] = true;
    }
    rasp.pop_back();
    for(auto x:rasp)
        cout << x << ' ';
    return 0;
}