#include <fstream>
#include <vector>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int n,nod,vecin,F[500100],D[500100],k,s[500100],m,x,y;
vector< pair<int,int> >L[500100];
int main(){
    fin>>n>>m;
    for(int 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]++;


    }
    for(int i=1;i<=m;i++){
       if(D[i]%2==1){
            fout<<"-1";
            return 0;
       }

    }
    k=1;
    s[k]=1;
    while(k!=0){
        nod=s[k];
        if(D[nod]==0){
            if(k>1){
                fout<<nod<<" ";
            }

            k--;
            continue;
        }
        while(F[L[nod].back().second]==1){
            L[nod].pop_back();

        }
        vecin=L[nod].back().first;
        D[nod]--;
        D[vecin]--;
        F[L[nod].back().second]=1;
        L[nod].pop_back();
        k++;
        s[k]=vecin;

    }
}