#include <bits/stdc++.h>
using namespace std;
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
int n, m, i, j, k, t, f, u, hi, lo, md;
cin >> n >> m;
vector<int> p(n, 0), o = {0}, d(n);
vector<vector<pair<int, bool> > > v(n);
for (k = 0; k < m; k++)
{
cin >> i >> j;
i--;
j--;
v[i].push_back({j, 0});
v[j].push_back({i, 0});
}
for (k = 0; k < n; k++)
{
d[k] = v[k].size();
sort(v[k].begin(), v[k].end());
}
t = f = 0;
vector<bool> w(n, 0);
w[0] = 1;
for (k = 1; k <= m; k++)
{
for (; p[t] < v[t].size(); p[t]++)
{
if (v[t][p[t]].second)
continue;
u = v[t][p[t]].first;
hi = v[u].size();
lo = -1;
while (hi - lo > 1)
{
md = (hi + lo) >> 1;
if (v[u][md].first > t)
hi = md;
else
lo = md;
}
v[u][lo].second = v[t][p[t]].second = 1;
d[t]--;
d[u]--;
//cout << "C " << t << " " << u << " " << d[t] << " " << d[u] << " " << w[u] << endl;
t = u;
if (w[t])
{
//cout << "B " << t << endl;
while (o.back() != t)
{
w[o.back()] = 0;
cout << o.back() + 1 << " ";
o.pop_back();
}
cout << t + 1 << endl;
if (o.size() == 1)
{
o.pop_back();
w[t] = 0;
while (f < n && (!d[f] || w[f]))
f++;
if (f == n)
break;
t = f;
o.push_back(t);
w[t] = 1;
//cout << "A " << t << endl;
}
}
else
{
//cout << "D " << t << endl;
w[t] = 1;
o.push_back(t);
}
break;
}
}
}
