#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename U> using ordered_map = tree<T, U, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<ll> vll;
#define FOR(i,j,k,in) for(int i=(j); i < (k);i+=in)
#define FORD(i,j,k,in) for(int i=(j); i >=(k);i-=in)
#define REP(i,b) FOR(i,0,b,1)
#define REPD(i,b) FORD(i,b,0,1)
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define all(x) begin(x), end(x)
#define MANY_TESTS int tcase; cin >> tcase; while(tcase--)
const double EPS = 1e-9;
const int MOD = 1e9+7;
const ll INFF = 1e18;
const int INF = 1e9;
const ld PI = acos((ld)-1);
const vi dy = {1, 0, -1, 0, -1, 1, 1, -1};
const vi dx = {0, 1, 0, -1, -1, 1, -1, 1};
void DBG(){cout << "]" << endl;}
template<typename T, typename ...U> void DBG(const T& head, const U... args){ cout << head << "; "; DBG(args...); }
#define dbg(...) cout << "Line(" << __LINE__ << ") -> [" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__);
#define chk() cout << "Check at line(" << __LINE__ << ") hit." << endl;
template<class T, unsigned int U>
ostream& operator<<(ostream& out, const array<T, U> &v){out << "["; REP(i, U) out << v[i] << ", "; out << "]"; return out;}
template <class T, class U>
ostream& operator<<(ostream& out, const pair<T, U> &par) {out << "[" << par.first << ";" << par.second << "]"; return out;}
template <class T>
ostream& operator<<(ostream& out, const set<T> &cont) { out << "{"; for( const auto &x:cont) out << x << ", "; out << "}"; return out; }
template <class T, class U>
ostream& operator<<(ostream& out, const map<T, U> &cont) {out << "{"; for( const auto &x:cont) out << x << ", "; out << "}"; return out; }
template<class T>
ostream& operator<<(ostream& out, const vector<T> &v){ out << "["; REP(i, v.size()) out << v[i] << ", "; out << "]"; return out;}
template<class T>
istream& operator>>(istream& in, vector<T> &v){ for(auto &x : v) in >> x; return in; }
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
// g[x] = {y, edge_id}
// m = number of edges in graph;
vector<int> find_eulerian_path(const vector<vector<array<int, 2>>> &g, int m, int s){
vector<bool> visited(m, false);
vector<int> ptr(g.size(), 0);
vector<int> stk, tour;
stk.push_back(s);
while(!stk.empty()){
bool found = false;
int v = stk.back();
while(ptr[v] < g[v].size()){
int id = g[v][ptr[v]][1];
if(visited[id]){
ptr[v]++; continue;
}
stk.push_back(g[v][ptr[v]][0]);
visited[id] = true; ptr[v]++;
found = true;
break;
}
if(!found){
tour.push_back(v);
stk.pop_back();
}
}
reverse(all(tour));
return tour;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
int n, m;
cin >> n >> m;
vector<vector<array<int, 2>>> g(n);
REP(i, m){
int u, v;
cin >> u >> v;
u--; v--;
g[u].pb({v, i});
g[v].pb({u, i});
}
vector<int> tour_res = find_eulerian_path(g, m, 0);
vector<bool> is_on_stack(n, false);
vector<int> st;
vector<vector<int>> ans;
REP(i, tour_res.size()){
if(is_on_stack[tour_res[i]]){
while(st.back() != tour_res[i]){
is_on_stack[st.back()] = false;
cout << st.back() + 1 << " ";
st.pop_back();
}
cout << st.back() + 1 << "\n";
}
else{
st.push_back(tour_res[i]);
is_on_stack[tour_res[i]] = true;
}
}
return 0;
}
