# include <bits/stdc++.h>
using namespace std;
ifstream fi("ciclueuler.in");
ofstream fo("ciclueuler.out");
const int nmax = 1e5 + 5;
vector < int > S[nmax];
int p[nmax];
int Sol[nmax];
bool b[nmax];
void dfs(int x)
{
    b[x]=1;
    for (int i=0;i<p[x];++i) if (!b[S[x][i]]) dfs(S[x][i]);
}
bool eulerian(int n)
{
    dfs(1);
    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);
    for (int i=1;i<=n;++i) p[i]=int(S[i].size());
    if (!eulerian(n)) return fo<<"-1\n",0;
    stack < int > s;
    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]];
            s.push(to);
            --p[v];S[v].pop_back();
            S[to].erase(find(S[to].begin,S[to].end(),v));
            p[to]=int(S[to].size());
            cout << "pidar\n";
        }
    }
    for (int i=1;i<Sol[0];++i) fo << Sol[i] << '\n';
}