#include <vector>
#include <algorithm>
#include <iostream>
#include <set>
#include <cmath>
#include <map>
#include <random>
#include <cassert>
#include <ctime>
#include <cstdlib>
#include <queue>
#include <limits.h>
using namespace std;
vector<vector<pair<int,int>>> adj;
vector<bool> hasVisited;
int main() {
//freopen("balancing.in", "r", stdin);
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int N, M; cin >> N >> M; adj.resize(N); hasVisited.assign(N, false);
vector<bool> okay(M);
for (int i = 0; i < M; i++) {
int u, v; cin >> u >> v; u--, v--;
adj[u].push_back({v, i}), adj[v].push_back({u, i});
}
okay.assign(M, true);
vector<pair<int,int>> nodes;
for (int i = 0; i < N; i++) {
nodes.push_back({i, -1});
while (!nodes.empty()) {
int cur = nodes.back().first;
int prev = nodes.back().second;
hasVisited[cur] = true;
bool upd = false;
for (pair<int,int> pr: adj[cur]) {
int j = pr.first;
if (pr.second == prev) {
continue;
}
if (!okay[pr.second]) {
continue;
}
if (hasVisited[j]) {
while (!nodes.empty() && nodes.back().first != j) {
hasVisited[nodes.back().first] = false;
cout << nodes.back().first + 1 << ' ';
okay[nodes.back().second] = false;
nodes.pop_back();
}
okay[pr.second] = false;
cout << j + 1 << ' ';
cout << '\n';
} else {
nodes.push_back({j, pr.second});
}
upd = true;
break;
}
if (!upd) {
nodes.pop_back();
}
}
}
}
