#include <cstdio>
#include <deque>
#define N 100010
#define M 500010
using namespace std;
deque <int> v[N];
int a[M],b[M],aux,i,n,m,gr[N];
bool viz[N],q[N];
void dfs(int nod)
{
    for(deque <int>::iterator it=v[nod].begin();it!=v[nod].end();it++)
    {
        int vec=a[*it]+b[*it]-nod;
        if(!viz[vec])
        {
            viz[vec]=1;
            q[*it]=1;
            dfs(vec);
        }
    }
}
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();ok=1;}
        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;
    dfs(1);
    for(i=1;i<=n;i++)
        if(!viz[i])
        {
            printf("-1\n");
            return 0;
        }
    go(1);
    return 0;
}