#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;;
#define ll long long
#define ar array
template<typename T>
using oset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
// #define int long long
#define all(v) v.begin(), v.end()
#define ld long double
const int N = 5e5 + 20;
const int M = 2;
const int LOG = 20;
const ll INF = 1e14;
int MOD = 998244353;
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
template<typename T>
inline void chmin(T &x,T y){x = min(x, y);}
template<typename T>
inline void chmax(T &x,T y){x = max(x, y);}
inline void mm(int &x){x = (x % MOD + MOD) % MOD;};
int n, m;
set<int> g[N];
vector<int> euler;
void dfs(int x){
while(g[x].size()){
int u = *g[x].begin();
g[x].erase(g[x].begin());
g[u].erase(x);
dfs(u);
}
euler.push_back(x);
}
void orz(){
cin>>n>>m;
for(int i = 0;i < m;i++){
int a, b;
cin>>a>>b;
--a, --b;
g[a].insert(b);
g[b].insert(a);
}
dfs(0);
bool vis[n] = {0};
vector<int> v;
for(auto u: euler){
if(vis[u]){
cout<<1 + u<<" ";
while(v.size() && v.back() != u){
cout<<v.back() + 1<<" ";
vis[v.back()] = 0;
v.pop_back();
}
cout<<'\n';
}else v.push_back(u), vis[u] = 1;
}
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int t = 1;
//cin>>t;
while (t--)orz();
}
//I am stupid :D
