// I stand with PALESTINE
// #pragma GCC optimize("Ofast,O3")
// #pragma GCC target("avx,avx2")
#include "bits/stdc++.h"
using namespace std;
using ll = long long;
const int M = 5e5 + 5, N = 5e5 + 5;
vector<bool> deleted(M);
vector<vector<pair<int, int>>> g(N);
vector<int> way;
void dfs(int u) {
while (!g[u].empty()) {
if (deleted[g[u].back().second]) {
g[u].pop_back();
continue;
}
deleted[g[u].back().second] = true;
dfs(g[u].back().first);
}
way.emplace_back(u);
}
void solve() {
int n, m;
cin >> n >> m;
for (int i = 0; i < m; i++) {
int u, v;
cin >> u >> v;
g[u].emplace_back(v, i);
g[v].emplace_back(u, i);
}
for (int i = 1; i <= n; i++) {
if (g[i].size() % 2) assert(false);
}
dfs(1);
if (way.size() < m + 1) assert(false);
vector<int> last(n + 1, -1), vec;
// for (int &x: way) cout << x << ' ';
// cout << endl;
for (int i = 0; i < way.size(); i++) {
vec.emplace_back(way[i]);
// cout << way[i] << ' ' << last[way[i]] << endl;
if (last[way[i]] != -1) {
cout << vec.back() << ' ';
vec.pop_back();
while (vec.back() != way[i]) {
last[vec.back()] = -1;
cout << vec.back() << ' ';
vec.pop_back();
}
cout << '\n';
} else {
last[way[i]] = i;
}
}
}
int main() {
cin.tie(0)->sync_with_stdio(false);
#ifdef sunnatov
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
int q = 1;
// cin >> q;
while (q--) {
solve();
// cout << '\n';
}
}
