#include <cstdio>
#include <deque>
#define N 100010
#define M 500010
using namespace std;
deque <int> v[N],w;
deque <int>::iterator it;
int viz[N],a[M],b[M],aux,i,n,m,gr[N],q[M];
void go(int nod)
{
    if(m){printf("%d\n",nod);m--;}
    else
        return;
    int aux;
    int ok=1;
    int nn=0;
    while(ok&&nn<v[nod].size())
    {
        ok=0;
        nn++;
        while(v[nod].size()&&!a[v[nod].back()]){v[nod].pop_back();}
        if(v[nod].size()&&q[v[nod].back()])
        {
            ok=1;
            aux=v[nod].back();
            v[nod].pop_back();
            v[nod].push_front(aux);
        }
    }

    if(v[nod].size())
    {
        int x=v[nod].back();
        v[nod].pop_back();
        int vec=a[x]+b[x]-nod;
        a[x]=0;
        go(vec);
    }
}
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d%d",&n,&m);
    for(i=1;i<=m;i++)
    {
        scanf("%d%d",&a[i],&b[i]);
        v[a[i]].push_back(i);
        v[b[i]].push_back(i);
        gr[a[i]]++;
        gr[b[i]]++;
    }
    for(i=1;i<=n;i++)
        if(gr[i]&1)
        {
            printf("-1\n");
            return 0;
        }
    viz[1]=1;
      viz[1]=1;
    w.push_back(1);
    while(w.size())
    {
        int x=w.front();
        w.pop_front();
        for(it=v[x].begin();it!=v[x].end();it++)
        {
            int vec=a[*it]+b[*it]-x;
            if(!viz[vec])
            {
                viz[vec]=1;
                q[*it]=1;
                w.push_back(vec);
            }
    }
    }
    for(i=1;i<=n;i++)
        if(!viz[i])
        {
            printf("-1\n");
            return 0;
        }
    go(1);
    return 0;
}