#include <fstream>
#include <vector>
using namespace std;
ifstream fin("ciclu_eulerian.in");
ofstream fout("ciclu_eulerian.out");
vector < pair <int,int> > v[100100];
int viz[500100],k,sol[1000100];

void ciclu(int s)
{
    int nod,muchie;
    while(!v[s].empty())
    {
        nod=v[s].back().first;
        muchie=v[s].back().second;
        v[s].pop_back();
        if(viz[muchie]==0)
        {
            viz[muchie]=1;
            ciclu(nod);
        }
    }
    k++;
    sol[k]=s;
}
int main()
{
    int n,m,x,y,i;
    fin>>n>>m;
    for(i=1;i<=n;i++)
    {
        fin>>x>>y;
        v[x].push_back({y,i});
        v[y].push_back({x,i});
    }
    for(i=1;i<=n;i++)
    {
        if(v[i].size()%2!=0)
        {
            fout<<-1;
            return 0;
        }
    }
    ciclu(1);
    for(i=1;i<k;i++)
    {
        fout<<sol[i]<<" ";
    }
    fin.close();
    fout.close();
    return 0;
}