#include <fstream>
#include <vector>
#include <stack>
#define NMAX 100002
#define MMAX 500002
using namespace std;

ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

struct varf{int x,nr;};
int n,m;
vector<varf> G[NMAX];
bool uz[MMAX];
int d[NMAX];
stack <int> S;
void citire();
int grade_pare();
void euler(int start);
int main()
{
    int i;
    int start,eulerian=-1;
    citire();
    if(!(start=grade_pare()))
        cout<<-1<<' ';
    else
        euler(start);
        for(i=1;i<=m;i++)
            if(!uz[i]) eulerian=0;
        if(!eulerian)
        {
            cout.close();
            cout.open("ciclueuler.out");
            cout<<-1<<'\n';
        }
    return 0;
}
void citire()
{
    varf vf;
    int i,x,y;
    cin>>n>>m;
    for(i=1;i<=m;i++)
    {
        cin>>x>>y;
        vf.x=y;vf.nr=i;
        G[x].push_back(vf);
        vf.x=x;vf.nr=i;
        G[y].push_back(vf);
        d[x]++;d[y]++;
    }
}
int grade_pare()
{
    int i,start;
    for(i=1;i<=n;i++)
        {if(d[i]%2) return 0;
    if(d[i]) start=i;}
    return start;
}
void euler(int start)
{
    varf vfad;
    int vf;
    S.push(start);
    while(!S.empty())
    {
        vf=S.top();
        if(!G[vf].empty())
        {
            vfad=G[vf][G[vf].size()-1];
            if(!uz[vfad.nr])
            {
                uz[vfad.nr]=1;
                S.push(vfad.x);
            }
            G[vf].pop_back();
        }
        else
            {cout<<' '<<vf; S.pop();}
    }
}