#include<bits/stdc++.h>
const int N = 5e5 + 5;
using namespace std;
typedef pair <int, int> ii;
set <int> adj[N];
vector <int> mv[N];
int n, m, a, b, cnt;
bool check[N], edge[N];
stack <int> ms;
void dfs(int u){
while (adj[u].size()){
int v = *adj[u].begin();
adj[u].erase(adj[u].begin()); adj[v].erase(u);
dfs(v);
}
if (check[u]){
while (ms.top() != u){
cout << ms.top() << " ";
check[ms.top()] = 0;
ms.pop();
}
cout << u << "\n";
ms.pop();
check[u] = 0;
}
check[u] = 1;
ms.push(u);
}
int main(){
//ios_base::sync_with_stdio(false); cin.tie(0);
cin >> n >> m;
for (int i = 0; i < m; i++) {
cin >> a >> b;
adj[a].insert(b);
adj[b].insert(a);
}
dfs(1);
}
