#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <stack>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int N,nr=0,M,adj[100010];
vector <int> v[100010],rez;
vector <pair <int,int> > a;
vector <bool> fv;
stack <int> st;
int prim,ok=1;
void euler()
{
    int aux,nod,p;
    while(!st.empty())
    {
        nod=st.top();

        if(!v[nod].empty())
        {
            aux=v[nod].back();
            v[nod].pop_back();
            if(fv[aux]==1)
            {
                fv[aux]=0;
                p=a[aux].second;
                if(p==nod)
                p=a[aux].first;
                st.push(p);
            }
        }
        else
        {
            rez.push_back(nod);
            st.pop();
        }
    }
}
int main()
{
    int x,y,i;
    fin>>N>>M;
    while(fin>>x>>y)
    {
        nr++;
        a.push_back(make_pair(x,y));
        fv.push_back(1);
        v[x].push_back(nr-1);
        v[y].push_back(nr-1);
        adj[x]++;
        adj[y]++;
    }
    for(i=1;i<=N;i++)
        if(adj[i]%2==1)
        ok=0;
    st.push(1);
    euler();
    x=rez.size();
    if(ok==0)
    {
        fout<<-1;
    }
    else
    for(i=0;i<x-1;i++)
    {
        fout<<rez[i]<<' ';
    }
}