#include <bits/stdc++.h>
using namespace std;
#define pb push_back
const int N = 5e5 + 5;
vector<array<int, 2>> g[N];
vector<int> e;
bool vis[N], vis2[N];
void dfs(int s) {
vis2[s] = 1;
while (!g[s].empty()) {
auto [u, w] = g[s].back(); g[s].pop_back();
if (vis[w]) continue;
vis[w] = 1;
dfs(u);
}
e.pb(s);
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n, m;
cin >> n >> m;
for (int i = 1; i <= m; ++i) {
int u, v;
cin >> u >> v;
g[u].pb({v, i}); g[v].pb({u, i});
}
for (int i = 1; i <= n; ++i) {
if (!vis2[i]) dfs(i);
}
vector<vector<int>> ans;
int f[n+1];
fill(f, f+n+1, 0);
stack<int> z;
for (int i = 0; i < e.size(); ++i) {
bool ok = 1;
if (f[e[i]]) {
ans.pb({e[i]});
while (z.top() != e[i]) {
ans.back().pb(z.top());
f[z.top()] = 0;
z.pop();
}
z.pop();
ok = 0;
}
z.push(e[i]), f[e[i]] = 1;
}
for (auto x : ans) {
for (auto y : x) {
cout << y << ' ';
}
cout << '\n';
}
}
