#include <fstream>
#include <vector>
#define nmax 100010
#include <list>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
vector <int> v[nmax];
list <int> q;
int viz[nmax],gr[nmax],ok,nr,n,m;
/*void df(int i)
{
    int j;
    viz[i]=1;nr++;
    for(j=0;j<v[i].size();j++)
    if(!viz[v[i][j]]) df(v[i][j]);
}*/
void euler(int i)
{
    int nod,vec,j;
    q.push_back(i);
    while(!q.empty())
    {
        nod=q.front();
        if(v[nod].empty())
        {
            q.pop_front();
            if(q.size()) g<<nod<<' ';
        }
        else
        {
        vec=v[nod].back();
        v[nod].pop_back();
        q.push_front(vec);
        int num=v[vec].size();
        for(j=0;j<num;j++)
        if(v[vec][j]==nod) {v[vec][j]=v[vec].back();v[vec].pop_back();break;}
        }
    }
}
int main()
{
    int i,x,y;
    f>>n>>m;
    for(i=1;i<=m;i++)
    {
        f>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
        gr[x]++;gr[y]++;
    }
    ok=1;
    for(i=1;i<=n&&ok;i++)
    if(gr[i]%2) ok=0;
    if(ok) /*df(1);
    if(nr==n)*/ euler(1);
    else g<<-1;
    return 0;
}