#include <fstream>
#include <vector>
#include <deque>

using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

bool viz[500002];
struct bla
{
    int no,mu;
};
vector <bla> graph[100002];
deque <int> q;
deque <int> :: reverse_iterator it;


void euler(int nod)
{
    for(int i=0;i<graph[nod].size();++i)
    {
        int ve=graph[nod][i].no;
        if(!viz[graph[nod][i].mu])
        {
            viz[graph[nod][i].mu]=1;
            euler(ve);
        }
    }
    q.push_back(nod);
}
int main()
{
    int n,m,x,y;
    f>>n>>m;
    for(int i=1;i<=m;++i)
    {
        f>>x>>y;
        graph[x].push_back({y,i});
        graph[y].push_back({x,i});
    }
    for(int i=1;i<=n;++i)
        if(graph[i].size()%2!=0)
        {
            g<<-1;
            return 0;
        }
    euler(1);
    q.pop_front();
    for(it=q.rbegin();it!=q.rend();++it)
        g<<*it<<' ';
    return 0;
}