#include <fstream>
#include <list>
#include <queue>
#include <stack>
#define DIM 100001

using namespace std;

ofstream out("ciclueuler.out");

stack <int> st;
queue <int> q;
list <int> nod[DIM];

short int vis[DIM];

int v, vf,a , b, n, mu, y, x;

void sterge()
{
    for( list <int>::iterator i=nod[vf].begin(); i!=nod[vf].end(); ++i)
        {
            if(*i==v)
            {
                nod[vf].erase(i);
                break;
            }
        }
}

void ciclu()
{
    st.push(1);
    while(!st.empty())
    {
        v=st.top();
        if(!nod[v].empty())
            {
                vf=nod[v].front();
                st.push(vf);
                nod[v].pop_front();
                sterge();
                continue;
            }
        st.pop();
        out<<v<<" ";
    }
}

int verif()
{
    q.push(1);
    vis[1]=1;
    while(!q.empty())
    {
        vf=q.front();
        for( list <int>::iterator i=nod[vf].begin(); i!=nod[vf].end(); ++i)
        {
            if(vis[*i]==0)
            {
                q.push(*i);
                vis[*i]=1;
            }
        }
        q.pop();
    }
    y=1;
    for(int i=1; i<=n; ++i)
    {
        if(vis[i]==0||nod[i].size()%2==1)
            {
                y=0;
                break;
            }
    }
    return y;
}

int main()
{
    ifstream in("ciclueuler.in");
    in>>n>>mu;
    for(int i=1; i<=mu; ++i)
    {
        in>>a>>b;
        nod[a].push_back(b);
        nod[b].push_back(a);
    }
    x=verif();
    if(x==1)
        ciclu();
    else out<<"-1\n";
    in.close();
    out.close();
    return 0;
}