#include<iostream>
#include<fstream>
#include<vector>
#include<queue>
#define DM 500100
#define DN 100100
using namespace std;
fstream fin("ciclueuler.in",ios::in),fout("ciclueuler.out",ios::out);
queue<int> qu;
vector<int> v[DN];

struct str
{
    int a,b,viz;
} much[DM];

int n,m;

void eulerian(int nod)
{
    int i,aux,urm;
    while(v[nod].size()!=0)
    {
        aux=v[nod].back();
        if(much[aux].viz==1)
        {
            v[nod].pop_back();
            continue;
        }
        urm=much[aux].a+much[aux].b-nod;
        much[aux].viz=1;
        eulerian(urm);
    }
    qu.push(nod);
    //cout<<nod<<" ";
}

int main()
{
    int a,b,i;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>a>>b;
        much[i]={a,b,0};
        v[a].push_back(i);
        v[b].push_back(i);
    }
    for(i=1;i<=n;i++)
    {
        if(v[i].size()%2==1)
        {
            fout<<"-1\n";
            return 0;
        }
    }
    eulerian(1);
    while(qu.size()>1)
    {
        fout<<qu.front()<<" ";
        qu.pop();
    }
}