#include <algorithm>
#include <vector>
#include <stack>
#include <list>
using namespace std;

#define pb push_back
#define pf pop_front
#define DIM 100005
#define er erase

int sol[DIM],grd[DIM],viz[DIM];
list <int> lst[DIM];
stack <int> st;
int n,m,nrt;

void read ()
{
    int i,x,y;

    scanf ("%d%d",&n,&m);
    for (i=1; i<=m; ++i)
    {
        scanf ("%d%d",&x,&y);
        ++grd[x];
        ++grd[y];
        lst[x].pb (y);
        lst[y].pb (x);
    }
}

int check ()
{
    int i;

    for (i=1; i<=n; ++i)
        if (grd[i]&1)
            return 0;
    return 1;
}

void euler ()
{
    list <int> :: iterator it;
    int i,nod,next;

    for (st.push (1); !st.empty (); )
    {
        nod=st.top ();
        if (lst[nod].empty ())
        {
            sol[++nrt]=nod;
            st.pop ();
        }
        else
        {
            st.push (*lst[nod].begin ());
            lst[nod].pf ();
            next=st.top ();
            for (it=lst[next].begin (); it!=lst[next].end (); ++it)
                if (*it==nod)
                {
                    lst[next].erase (it);
                    break;
                }
        }

    }
    for (i=1; i<nrt; ++i)
        printf ("%d ",sol[i]);
}

int main ()
{
    freopen ("ciclueuler.in","r",stdin);
    freopen ("ciclueuler.out","w",stdout);

    read ();
    if (check ())
        euler ();
    else
        printf ("-1");

    return 0;
}