#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/tree_policy.hpp> // Including tree_order_statistics_node_update
using namespace std;
#define ll long long
#define ull unsigned long long
#define ld long double
#define pb push_back
void dbg_out() { cout << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cout << ' ' << H; dbg_out(T...); }
#define dbg(...) cout << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
vector<vector<ll>> adj;
vector<ll> euler;
stack<ll> st;
unordered_map<ll,ll> cnt;
vector<unordered_map<ll,bool>> vis;
void dfs(ll u){
for(auto v : adj[u]){
if(!vis[u][v]){
vis[u][v]=true; vis[v][u]=true;
dfs(v);
}
}
euler.pb(u);
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
ll n,m,u,v;
cin >> n >> m;
adj.assign(n+1, {});
vis.assign(n+1, {});
for(ll i = 0; i < m; i++){
cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
}
dfs(1);
// for(auto el : euler) cout << el << " ";
// cout << endl << endl;
for(auto el : euler){
if(cnt[el] > 0){
while(st.top() != el){
cnt[st.top()]--;
cout << st.top() << " ";
st.pop();
}
cout << st.top() << endl;
} else{
st.push(el);
cnt[el]++;
}
}
}
