#include<fstream>
#include<algorithm>
#include<list>
#include<deque>
#define N 100010
using namespace std;
ofstream g("ciclueuler.out");
list<int> v[N];
list<int>::iterator it;
deque<int> Q;
int n,m,i,x,y,ok;
void euler(int nd)
{
    int nod,nod2;
    Q.push_front(nd);
    while(!Q.empty())
    {
        nod=Q.front();
        if(v[nod].size()==0)
        {
            g<<nod<<" ";
            Q.pop_front();
            continue;
        }
        nod2=v[nod].back();
        v[nod].pop_back();
        Q.push_front(nod2);
        for(it=v[nod2].begin(); it!=v[nod2].end(); it++)
            if(*it == nod)
            {
                v[nod2].erase(it);
                break;
            }
    }
}
int main()
{
    ifstream f("ciclueuler.in");
    f>>n>>m;
    for(i=1; i<=m; i++)
    {
        f>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    ok=1;
    for(i=1; i<=n; i++) if(v[i].size()%2)
        {
            ok=0;
            break;
        }

    if(!ok)g<<-1<<"\n";
    else  euler(1);
    f.close();
    g.close();
    return 0;
}