#include <bits/stdc++.h>
using namespace std;
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
using ll = long long;
const ll MAXN = 500005, MAXM = 500005;
vector<pair<ll, ll>> edges[MAXN];
bool vis[MAXM];
vector<ll> path;
ll st[MAXN];
void dfs(ll v) {
while (!edges[v].empty()) {
auto[u, id] = edges[v].back();
edges[v].pop_back();
if (vis[id]) continue;
vis[id] = 1;
dfs(u);
}
path.push_back(v);
st[v]++;
if (st[v] == 2) {
st[v]--;
path.pop_back();
cout << v+1 << ' ';
while (path.back() != v) {
cout << path.back()+1 << ' ';
st[path.back()]--;
path.pop_back();
}
cout << '\n';
}
}
void solve() {
ll n, m;
cin >> n >> m;
for (ll i = 0; i < m; i++) {
ll v, u;
cin >> v >> u;
v--, u--;
edges[v].push_back({u, i});
edges[u].push_back({v, i});
}
dfs(0);
// for (ll x : path) cout << x+1 << ' ';
// cout << '\n';
}
int main() {
// freopen("promote.in", "r", stdin);
// freopen("promote.out", "w", stdout);
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
solve();
}
