#include <fstream>
#include <vector>
#include <algorithm>
#define Nmax 100010
#define Mmax 500010
using namespace std;
long n,m;
vector <pair<long,long> > v[Nmax];
int f[Mmax];
vector <long> ans,h;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int main()
{

    fin>>n>>m;
    for(int i=1;i<=m;i++)
    {
        int x,y;
        fin>>x>>y;
        v[x].push_back(make_pair(i,y));
        v[y].push_back(make_pair(i,x));

    }

    for(int i=1;i<=n;i++)
        if(v[i].size()%2!=0)
        {
            fout<<"-1\n";
            return 0;
        }


    long nod,muchie,son;
    h.push_back(1);
    while(!h.empty())
    {   nod=h.back();
        if(!v[nod].empty())
        {
            muchie=v[nod].back().first;
            son=v[nod].back().second;
            v[nod].pop_back();
            if(f[muchie]) continue;
            f[muchie]=1;
            h.push_back(son);

        }
        else
        {
            h.pop_back();
            ans.push_back(nod);
        }


    }

    for(int i=0;i<ans.size();i++)
        fout<<ans[i]<<' ';
    return 0;
}