/* Author: goats_9 */
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
class DSU {
int n;
vector<int> p, rank;
vector<pair<int, int>> bridge;
public:
DSU (int _n) : n(_n), p(n), rank(n), bridge(n, {-1, -1}) { iota(p.begin(), p.end(), 0); }
int get(int i) { return (p[i] == i) ? p[i] : (p[i] = get(p[i])); }
void unite(int i, int j) {
i = get(i), j = get(j);
if (i == j) {
bridge[i] = {-1, -1};
return;
}
if (rank[i] < rank[j]) swap(i, j);
if (rank[i] == rank[j]) ++rank[i];
p[j] = i;
bridge[j] = {i, j};
}
void bridges() {
for (auto [u, v] : bridge) {
if (u == -1) continue;
cout << u + 1 << ' ' << v + 1 << '\n';
}
}
};
int main() {
cin.tie(0)->sync_with_stdio(0);
int n, m;
cin >> n >> m;
DSU dsu(n);
for (int i = 0; i < m; i++) {
int u, v;
cin >> u >> v;
dsu.unite(--u, --v);
}
dsu.bridges();
return 0;
}
