#include <bits/stdc++.h>
using namespace std;
#define fast ios::sync_with_stdio(0);cin.tie(0);
typedef long long ll;
#define f first
#define s second
#define MOD 1000000007
#define LOGN 20
#define MAXN 300005
vector<vector<pair<int,int>>> graph;
vector<pair<int,int>> edges;
vector<int> pathVis;
bool active(int i) {
if (edges[i].f == -1)
return false;
return true;
}
void deactivate(int i) {
edges[i].f = edges[i].s = -1;
}
int go_back = 0;
void dfs(int node, int parent) {
pathVis[node] = true;
for (auto u : graph[node]) {
if (u.f == parent || !active(u.s))
continue;
if (pathVis[u.f]) {
cout << u.f << " ";
go_back = u.f;
deactivate(u.s);
pathVis[node] = false;
} else
dfs(u.f, node);
if (go_back) {
if (go_back == node) {
go_back = 0;
deactivate(u.s);
cout << "\n";
continue ;
}
cout << node << " ";
deactivate(u.s);
pathVis[node] = false;
return ;
}
}
pathVis[node] = false;
}
int main() {
fast
int N, M, a, b;
cin >> N >> M;
graph = vector<vector<pair<int,int>>>(N+1, vector<pair<int,int>>());
pathVis = vector<int>(N+1, false);
for (int i = 0; i < M; i++) {
cin >> a >> b;
edges.push_back({a, b});
graph[a].push_back({b, edges.size()-1});
graph[b].push_back({a, edges.size()-1});
}
for (int i = 1; i <= N; i++)
dfs(i, i);
}
