#include <bits/stdc++.h>
#define mmax 500001
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
///ciclu eulerian-un ciclu simplu care contine toate muchiile.
///-ca un graf sa fie graf eulerian el trebuie sa fie conex si toate nodurile sale sa aiba valori pare.
int n,m,st[mmax],dt[mmax],viz[mmax],sol[mmax],k;
vector<int>h[mmax];
void Citire()
{
    int i;
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>st[i]>>dt[i];
        h[st[i]].push_back(i);
        h[dt[i]].push_back(i);
    }
}
inline bool Toate_Pare()
{
    int i;
    for(i=1;i<=n;i++)
        if(h[i].size()%2)return false;
    return true;
}
void DFS(int varf)
{
    int i,x;
    for(i=0;i<h[varf].size();i++)
        if(!viz[h[varf][i]])
    {
        x=h[varf][i];
        viz[x]=1;
        DFS(st[x]+dt[x]-varf);
    }
    sol[++k]=varf;
}
int main()
{
    int i;
    Citire();
    if(!Toate_Pare())
        fout<<"-1\n";
    else
    {
        DFS(1);
        for(i=1;i<k;i++)
            fout<<sol[i]<<" ";
        fout<<"\n";
    }
    fout.close();
    return 0;
}