#include <bits/stdc++.h>
#include <fstream>
#define cin fin
#define cout fout
using namespace std;
ifstream cin ("ciclueuler.in");
ofstream cout ("ciclueuler.out");
struct element
{
    int a,b;
    bool uz;
};
element muchie[500008];
vector<int>G[100008];
vector<int>stackk;
vector<int>sol;
int k,muc,n,m,i,a,b,frec[100008];
void euler(int nod)
{
    stackk.push_back(nod);
    while(!stackk.empty())
    {
        k=stackk.back();
        if(G[k].empty())
        {
            sol.push_back(k);
            stackk.pop_back();
        }
        else
        {
            muc=G[k].back();
            G[k].pop_back();
            if(muchie[muc].uz==1)
            {
                muchie[muc].uz=0;
                if(muchie[muc].a==k)
                    stackk.push_back(muchie[muc].b);
                else
                    stackk.push_back(muchie[muc].a);
            }
        }
    }
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cin>>n>>m;
    for(i=1; i<=m; i++)
    {
        cin>>a>>b;
        G[a].push_back(i);
        G[b].push_back(i);
        muchie[i]= {a,b,1};
        frec[a]++;
        frec[b]++;
    }
    for(i=1; i<=n; i++)
    {
        if(frec[i]==0 || frec[i]%2==1)
        {
            cout<<"-1";
            exit(0);
        }
    }
    euler(1);
    sol.pop_back();
    for(auto i:sol)
        cout<<i<<" ";
    return 0;
}