#include <bits/stdc++.h>
using namespace std;
int in[500010],sf[500010],i,x,y,m,n,nod,muchie;
vector<int>v[100010],st,ans;
bool ap[500010];
int main()
{
    ifstream f ("ciclueuler.in");
    ofstream g ("ciclueuler.out");
    f>>n>>m;
    for(i=1; i<=m; ++i)
    {
        f>>x>>y;
        v[x].push_back(i);
        v[y].push_back(i);
        in[i]=x;
        sf[i]=y;
    }
    for(i=1; i<=n; ++i)
        if(v[i].size()%2==1)
        {
            g<<-1;
            return 0;
        }
    st.push_back(1);
    while(!st.empty())
    {
        nod=st.back();
        if(v[nod].size()!=0)
        {
            muchie=v[nod].back();
            v[nod].pop_back();
            if(ap[muchie])continue;
            else
            {
                ap[muchie]=true;
                if(in[muchie]==nod)st.push_back(sf[muchie]);
                else st.push_back(in[muchie]);
            }
        }
        else
        {
            st.pop_back();
            ans.push_back(nod);
        }
    }
    for(i=0; i<ans.size()-1; ++i)
        g<<ans[i]<<" ";
    return 0;
}