#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
const int N = 100000;
int ii[N], jj[N]; bool bridge[N];
int ds[N], ds_[N], hh[N], dd[N];
vector<int> *eh[N]; bool visited[N];
int find(int i) {
return ds[i] < 0 ? i : (ds[i] = find(ds[i]));
}
void join(int i, int j) {
i = find(i);
j = find(j);
if (i == j)
return;
if (ds[i] == ds[j])
ds[i]--;
if (ds[i] < ds[j])
swap(i, j);
ds[i] = j;
if (hh[j] != -1 && !bridge[hh[j]])
hh[j] = hh[i];
dd[j] = min(dd[j], dd[i]);
for (int &h : *eh[i])
eh[j]->push_back(h);
delete eh[i];
}
int find_(int i) {
return ds_[i] < 0 ? i : (ds_[i] = find_(ds_[i]));
}
void dfs(int h_, int i, int d) {
hh[i] = h_, dd[i] = d++;
for (auto it = eh[i]->begin(); it != eh[i]->end(); ) {
int &h = *it, j = i ^ find(ii[h]) ^ find(jj[h]);
if (j == i) {
swap(h, *eh[i]->rbegin());
eh[i]->pop_back();
continue;
}
if (h != h_)
dfs(h, j, d);
it++;
}
}
bool join_(int i, int j, int h) {
int i_ = i; i = find_(i);
int j_ = j; j = find_(j);
if (i == j)
return false;
if (ds_[i] == ds_[j])
ds_[i]--;
if (ds_[i] < ds_[j])
swap(i, j), swap(i_, j_);
ds_[i] = j;
i = i_, j = j_;
bridge[h] = true;
eh[i]->push_back(h);
eh[j]->push_back(h);
dfs(h, i, dd[j] + 1);
return true;
}
int main() {
ios_base::sync_with_stdio(false), cin.tie(NULL);
int n, m; cin >> n >> m;
int m_ = 0;
for (int i = 0; i < n; i++)
ds[i] = ds_[i] = hh[i] = -1, eh[i] = new vector<int>;
while (m--) {
int i, j; cin >> i >> j, i--, j--;
ii[m_] = i, i = find(i);
jj[m_] = j, j = find(j);
if (join_(i, j, m_)) {
m_++;
continue;
}
while (i != j) {
if (dd[i] < dd[j])
swap(i, j);
int h = hh[i]; bridge[h] = false;
int p = i ^ find(ii[h]) ^ find(jj[h]);
join(i, p), i = find(i), j = find(j);
}
}
for (int h = 0; h < m_; h++)
if (bridge[h])
cout << ii[h] + 1 << ' ' << jj[h] + 1 << '\n';
return 0;
}
