#include <bits/stdc++.h>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
//#define int long long
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int mod = 1e9 + 7;
const int LOG = 20;
const int maxn = 5e5 + 5;
int n, m;
vector<pii> graph[maxn+5];
vector<int> P, vis(maxn), cnt(maxn);
void dfs(int u) {
while(!graph[u].empty()) {
auto [v, id] = graph[u].back();
graph[u].pop_back();
if(vis[id]) continue;
vis[id] = 1;
dfs(v);
}
cnt[u]++;
P.push_back(u);
if(cnt[u] == 2) {
cout << u << " ";
P.pop_back();
while(!P.empty() && P.back() != u) {
cout << P.back() << " ";
cnt[P.back()]--;
P.pop_back();
}
cnt[u]--;
cout << '\n';
}
}
signed main() {
ios_base::sync_with_stdio(false);
cout.tie(0); cin.tie(0);
cin >> n >> m;
for(int i=0; i<m; i++) {
int a, b;
cin >> a >> b;
graph[a].push_back({ b, i });
graph[b].push_back({ a, i });
}
dfs(1);
return 0;
}
