#include <bits/stdc++.h>

using namespace std;

ifstream fin ("ciclueuler.in");
ofstream fout ("ciclueuler.out");

#define lim 100010
int n,m,dr,newn;
list <int> G[lim];
int st[5*lim];
bool viz[lim];

void euler (int nod)
{
    while (!G[nod].empty())
    {
        newn = G[nod].front();
        G[nod].pop_front();
        G[newn].erase (find (G[newn].begin(), G[newn].end(), nod));
        euler (newn);
    }
    st[++dr]=nod;
}

int main()
{
    int a,b;
    fin>>n>>m;
    for (int i=1; i<=m; i++)
    {
        fin>>a>>b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

    for (int i=1; i<=n; i++)
        if (G[i].size()==0 || G[i].size()%2)
        {
            fout<<-1;
            return 0;
        }

    euler (1);
    for (int i=1; i<=m; i++)    fout<<st[i]<<' ';

    fout.close();
    return 0;
}