#include <bits/stdc++.h>
#define nmax 100001
#define mmax 500001
using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

vector<int> adj[nmax];
bool del[mmax];
int a[mmax],b[mmax];
int n,m;
void cic(int nod,bool first=0)
{
    while(adj[nod].size()>0)
    {
        int ed=adj[nod].back();
        adj[nod].pop_back();
        if(del[ed]) continue;
        //cout<<nod<<','<<ed<<','<<a[ed]<<','<<b[ed]<<'\n';
        del[ed]=1;
        if(a[ed]==nod) cic(b[ed]);
        else cic(a[ed]);
    }
    if(!first)
    g<<nod<<' ';
}

int main()
{
    f>>n>>m;
    for(int i=0;i<m;i++)
    {
        f>>a[i]>>b[i];
        adj[a[i]].push_back(i);
        adj[b[i]].push_back(i);
    }
    bool ok=1;
    for(int i=1;i<=n;i++) if(adj[i].size()%2!=0) ok=0;
    if(!ok) g<<-1;
    else cic(1,1);
    return 0;
}