#include <bits/stdc++.h>
using namespace std;
struct Edge
{
unsigned u, v, i, j; // u <-> i, v <-> j;
Edge(unsigned u_, unsigned v_, unsigned i_, unsigned j_)
{
u = u_, v = v_, i = i_, j = j_;
}
};
vector<vector<Edge>> g;
vector<bool> visited;
void delete_edge(Edge e)
{
swap(g[e.u][e.i], g[e.u].back());
swap(g[e.v][e.j], g[e.v].back());
g[e.u].erase(g[e.u].end() - 1);
g[e.v].erase(g[e.v].end() - 1);
if (e.i < g[e.u].size())
{
g[e.u][e.i].i = e.i;
g[g[e.u][e.i].v][g[e.u][e.i].j].j = e.i;
}
if (e.j < g[e.v].size())
{
g[e.v][e.j].i = e.j;
g[g[e.v][e.j].v][g[e.v][e.j].j].j = e.j;
}
}
unsigned get_next_edge(unsigned u, unsigned p)
{
for (size_t i = 0; i < g[u].size(); i++)
if (g[u][i].v != p)
return i;
}
Edge find_edge(unsigned u, unsigned v)
{
for (Edge const &e : g[u])
if (e.v == v)
return e;
}
unsigned find_circuit(unsigned u, unsigned p = -1)
{
if (visited[u])
return u;
visited[u] = 1;
assert(!g[u].empty());
Edge e = g[u][get_next_edge(u, p)];
unsigned x = find_circuit(e.v, u);
visited[u] = 0;
if (x != UINT_MAX)
{
cout << u + 1 << ' ' << flush;
delete_edge(find_edge(u, e.v));
if (u == x)
x = UINT_MAX;
}
return x;
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
size_t n, m;
cin >> n >> m;
g = vector<vector<Edge>>(n);
visited = vector<bool>(n, 0);
for (size_t i = 0; i < m; i++)
{
unsigned u, v;
cin >> u >> v;
u--, v--;
g[u].emplace_back(u, v, g[u].size(), g[v].size());
g[v].emplace_back(v, u, g[v].size(), g[u].size() - 1);
}
for (unsigned u = 0; u < n; u++)
{
while (!g[u].empty())
{
find_circuit(u);
cout << '\n';
}
}
}
