# include <bits/stdc++.h>
# define p(x) int(S[x].size())
using namespace std;
ifstream fi("ciclueuler.in");
ofstream fo("ciclueuler.out");
const int nmax = 1000010;
stack < int > s;
vector < int > S[nmax];
int Sol[nmax];
bool b[nmax];
void bfs()
{
    queue < int > q;
    q.push(1);
    while (q.size())
    {
        int v=q.front();q.pop();
        for (vector < int > ::iterator i=S[v].begin();i!=S[v].end();++i) if (!b[*i]) q.push(*i),b[*i]=1;
    }
}
bool eulerian(int n)
{
    bfs();
    for (int i=1;i<=n;++i) if (!b[i] || (p(i) & 1)) return 0;
    return 1;
}
int main(void)
{
    int n,m;
    fi>>n>>m;
    int x,y;
    while (m--) fi>>x>>y,S[x].push_back(y),S[y].push_back(x);
    if (!eulerian(n)) return fo<<"-1\n",0;
    s.push(1);
    while (s.size())
    {
        int v=s.top();
        if (!p(v)) Sol[++Sol[0]]=v,s.pop();
        else
        {
            int to=S[v][p(v)-1];
            s.push(to);
            S[v].pop_back();
            S[to].erase(find(S[to].begin(),S[to].end(),v));
        }
    }
    for (int i=1;i<Sol[0];++i) fo << Sol[i] << ' ';
    return 0;
}