#include <vector>
#include <algorithm>
#include <fstream>
using namespace std;
/// /g/ salutes you
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

const int nmax=100005;
vector <int> stiv;
vector <int> a[nmax];

int n,m;

void euler ()
{
    int nod,vecin;
    stiv.push_back(nod);

    while (!stiv.empty())
    {
        nod=stiv.back();
        if (a[nod].size())
        {
            vecin=a[nod].back();
            a[vecin].erase(find(a[vecin].begin(),a[vecin].end(),nod));
            a[nod].pop_back();
            stiv.push_back(vecin);
        }
        else
        {
            g<<nod<<" ";
            stiv.pop_back();
        }
    }
}

int main()
{
    int i,x,y;

    f>>n>>m;
    for (i=1;i<=m;i++)
    {
        f>>x>>y;
        a[x].push_back(y);
        a[y].push_back(x);
    }

    for (i=1;i<=n;i++)
    {
        if (a[i].size()%2 || a[i].size()==0)
        {
            g<<"-1";
            return 0;
        }
    }

    euler();

    return 0;
}