#include <fstream>
#include <vector>
using namespace std;
ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

int n,m,i,j,nr,x,y;
vector <pair<int,int>> v[100005], mu;
int a[100005];
int viz[500005];
int sol[500005];
int stiva[500005];
int stlev;

void euler()
{
    /*for(int i=0;i<v[nod].size();++i)
    {
        if(viz[v[nod][i].second] == 0 ) {
                viz[v[nod][i].second]=1;
                euler(v[nod][i].first);
                }
    }

    sol[++nr]=nod;
    */
    bool ok=0;
    stlev=1;
    stiva[1]=1;
    while(stlev>0)
    {
       int nod=stiva[stlev];
        ok=0;
        for(int i=0; i<v[nod].size(); ++i)
        {
            if(viz[v[nod][i].second] == 0 )
            {
                viz[v[nod][i].second]=1;
                stiva[++stlev]=v[nod][i].first;
                ok=1;
                break;
            }
        }
        if(ok==0)
        sol[++nr]=nod, --stlev;

    }

}

int main()
{
    cin>>n>>m;
    for(i=1; i<=m; ++i)
    {
        cin>>x>>y;
        v[x].push_back(make_pair(y,i-1));
        v[y].push_back(make_pair(x,i-1));
        mu.push_back(make_pair(x,y));
        ++a[x];
        ++a[y];
    }

    for(i=1; i<=n; ++i)
        if(a[i]%2==1)
        {
            cout<<"-1";
            return 0;
        }


    euler();

    for(i=1; i<nr; ++i)
    {
        //cout<<mu[sol[i]].first<<" "<<mu[sol[i]].second<<" ";
        cout<<sol[i]<<" ";
    }
    return 0;
}