#include <fstream>
#include <vector>
using namespace std;

ifstream fin ("ciclueuler.in");
ofstream fout("ciclueuler.out");

int n,m,i,j,x,y,k,st[200005],D[100005],ok,nod,vecin;
vector<int> F,v;
vector< pair<int, int> > L[100005];

int main(){
    fin>>n>>m;
    for (i=1;i<=m;i++){
        fin>>x>>y;
        L[x].push_back(make_pair(y,i));
        L[y].push_back(make_pair(x,i));
        D[x]++;
        D[y]++;
        F.push_back(0);
    }
    F.push_back(0);
    ok=1;
    for (i=1;i<=n && ok;i++)
        if (D[i]%2 || D[i]==0)
            ok=0;
    if (!ok)
        fout<<-1;
    else{
        st[++k]=1;
        while (k!=0){
            nod=st[k];
            if (D[nod]==0){
                v.push_back(nod);
                k--;
                continue;
            }
            while (F[L[nod].back().second]==1)
                L[nod].pop_back();
            vecin=L[nod].back().first;
            F[L[nod].back().second]=1;
            L[nod].pop_back();
            D[nod]--;
            D[vecin]--;
            st[++k]=vecin;
        }
        for (i=0;i<v.size()-1;i++)
            fout<<v[i]<<" ";
    }
    fin.close();
    fout.close();
    return 0;
}