#include<fstream>
#include<stack>
#include<vector>
#include<algorithm>
#define pb push_back
#define N 100001
using namespace std;
ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");
int i,j,m,n,x,y,viz[5*N],nou,l[5*N],nr;
stack <int> stiva;
vector <int> G[N];
void euler(int nod)
{
    stiva.push(nod);
    while(!stiva.empty())
    {
        nod=stiva.top();
        l[nod]=G[nod].size();
        if(l[nod])
        {
            nou=G[nod].back();
            stiva.push(nou);
            G[nou].erase(find(G[nou].begin(),G[nou].end(),nod));
            G[nod].pop_back();
        }
        else
        {
            viz[++nr]=nod;
            stiva.pop();
        }
    }
}
int main()
{
    cin>>n>>m;
    for(i=1;i<=m;i++)
    {
        cin>>x>>y;
        G[x].pb(y);
        G[y].pb(x);
    }
    for(i=1;i<=n;i++)
    {
        l[i]=G[i].size();
        if(l[i] & 1)
        {
            cout<<-1;
            return 0;
        }
    }
    for(i=1;i<=n and !l[i];i++);
    euler(i);
    for(i=1;i<=nr;i++)
        cout<<viz[i]<<" ";
    return 0;
}