#include <bits/stdc++.h>
#define endl '\n'
#define mod 1000000007
using namespace std;
vector<int> path;
void DFS(vector<pair<int,int>> adjList[], int u, vector<bool> &edge, vector<int> &visited) {
while (!adjList[u].empty()) {
int v = adjList[u].front().first;
int pos = adjList[u].front().second;
adjList[u].erase(adjList[u].begin());
if (edge[pos]) continue;
edge[pos] = true;
DFS(adjList,v,edge,visited);
}
path.push_back(u);
visited[u]++;
if (visited[u] == 2) {
cout << u + 1 << " ";
path.pop_back();
while (path.back() != u) {
cout << path.back() + 1 << " ";
visited[path.back()]--;
path.pop_back();
}
visited[u] = 1;
cout << endl;
}
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
int n, m; cin >> n >> m;
vector<pair<int,int>> adjList[n];
for (int i = 0; i < m; i++) {
int u, v; cin >> u >> v;
adjList[u-1].push_back({v-1,i});
adjList[v-1].push_back({u-1,i});
}
vector<bool> edge(m,false);
vector<int> visited(n,0);
DFS(adjList,0,edge,visited);
return 0;
}
