#include <bits/stdc++.h>
#define ll long long
#define pb push_back
#define pf push_front
#define mp make_pair
using namespace std;
const int maxn = 500100;
class edge {
public:
int nxt_node;
list<edge>::iterator reverse_edge;
edge(int _node) {
nxt_node = _node;
}
};
list<edge>adj[maxn];
int n, m;
vector<int>euler_tour;
bool visited[maxn];
void solve(int node) {
while(adj[node].size() > 0) {
edge x = adj[node].front();
int nxt = x.nxt_node;
adj[nxt].erase(x.reverse_edge);
adj[node].pop_front();
solve(nxt);
}
euler_tour.pb(node);
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cin>>n>>m;
int a, b;
for(int i=0;i<m;i++) {
cin>>a>>b;
adj[a].pf(edge(b));
list<edge>::iterator it_a = adj[a].begin();
adj[b].pf(edge(a));
list<edge>::iterator it_b = adj[b].begin();
it_a->reverse_edge = it_b;
it_b->reverse_edge = it_a;
}
solve(1);
vector<int>seq;
for(int i:euler_tour) {
//cout<<i<<" ";
if(!visited[i]) {
seq.pb(i);
visited[i] = true;
}
else {
// go back in seq while you find i
while(seq.size() > 0 && seq.back() != i) {
visited[seq.back()] = false;
cout<<seq.back()<<" ";
seq.pop_back();
} cout<<i<<"\n";
}
}
}
