#include<fstream>
#include<vector>
#include<deque>
using namespace std;
ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");

int n,m,x,y,i,nod,nod2,ok;
vector<int> a[100001];
deque<int> Q;
vector<int>::iterator it;

void euler()
{
    Q.push_front(1);
    while (!Q.empty())
    {
        nod=Q.front();

        if (a[nod].empty())
        {
            Q.pop_front();
            out<<nod<<' ';
            continue;
        }

        nod2=a[nod].back();
        Q.push_front(nod2);

        a[nod].pop_back();
        for (it=a[nod2].begin();it!=a[nod2].end();it++)
            if (*it==nod)
            {
                a[nod2].erase(it);
                break;
            }
    }
}

int main()
{
    in>>n>>m;
    for (i=1;i<=m;i++)
    {
        in>>x>>y;
        a[x].push_back(y);
        a[y].push_back(x);
    }
    for (i=1;i<=n;i++)
        if (a[i].size()%2) ok=1;
    if (ok) out<<"-1\n";
        else euler();
}