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

const int Nmax = 100010;

typedef vector<int>::iterator IT;
typedef list< pair<int,int> >::iterator LT;

vector<int> A[Nmax];
int Grad[Nmax],Marked[Nmax];
int N,M;

list< pair<int,int> > C, Sol;

ifstream F("ciclueuler.in");
ofstream G("ciclueuler.out");

void Get( int Nod )
{
    Grad[Nod] = A[Nod].size();
    Marked[Nod] = 1;
    for ( IT it=A[Nod].begin();it!=A[Nod].end();++it )
        if ( !Marked[ *it ] )
            Get( *it );
}

int Ok()
{
    for ( int i=1;i<=N;++i )
        if ( A[i].size() && !Marked[i] )
            return i;
    return -1;
}

void Elimin( int a , int b )
{
    for ( int i=0;i<int( A[a].size() );++i )
        if ( A[a][i] == b )
        {
            swap( A[a][i] , A[a].back() );
            A[a].pop_back();
            break;
        }
    for ( int i=0;i<int( A[b].size() );++i )
        if ( A[b][i] == a )
        {
            swap( A[b][i] , A[b].back() );
            A[b].pop_back();
            break;
        }
}

int main()
{
    F>>N>>M;
    for ( int i=0,x,y;i<M;++i )
    {
        F>>x>>y;
        A[x].push_back( y );
        A[y].push_back( x );
    }

    Get( 1 );
    for ( int i=1;i<=N;++i )
        if ( Marked[i]==0 || Grad[i]&1 )
        {
            G<<"-1\n";
            return 0;
        }

    Marked[1]=0;
    for ( int Nod=Ok(),Last,Init; Nod != -1 ;Nod = Ok() )
    {
        Marked[Nod]=0;
        Init = Nod;
        Last = Nod;
        Marked[Nod]=0;
        Nod = A[Nod].back();
        C.push_back( make_pair(Last,Nod) );
        Elimin( Last,Nod );

        while ( Nod != Init )
        {
            Marked[Nod]=0;
            Last = Nod;
            Nod = A[Nod].back();
            C.push_back( make_pair(Last,Nod) );
            Elimin( Last,Nod );
        }

        if ( Sol.empty() )
            C.splice(Sol.begin(),C);
        else
            for ( LT it=Sol.begin();it!=Sol.end();++it)
                if ( it->first == C.rbegin()->second )
                {
                    C.splice(it,C);
                    break;
                }
    }

    G<<Sol.begin()->first;
    for ( LT it=Sol.begin();it!=Sol.end();++it)
        G<<' '<<it->second;
    G<<'\n';

    return 0;
}