#include <bits/stdc++.h>
using namespace std;
int p1[100000], p2[100000], sz1[100000], sz2[100000];
vector<int> adj[100000];
bool v[100000];
int dep[100000], low[100000];
int root1(int x) {
if(p1[x] == x) return x;
else return p1[x] = root1(p1[x]);
}
void merge1(int a, int b) {
int x = root1(a), y = root1(b);
if(x == y) return;
if(sz1[x] < sz1[y]) swap(x, y);
p1[y] = x;
sz1[x] += sz1[y];
}
int root2(int x) {
if(p2[x] == x) return x;
else return p2[x] = root2(p2[x]);
}
void merge2(int a, int b) {
int x = root2(a), y = root2(b);
if(x == y) return;
if(sz2[x] < sz2[y]) swap(x, y);
p2[y] = x;
sz2[x] += sz2[y];
}
void dfs(int x, int d, int par) {
v[x] = 1;
low[x] = dep[x] = d;
bool f = true;
for(int i : adj[x]) {
if(i == par && f) {
f = false;
continue;
} else if(v[i]) {
low[x] = min(low[x], dep[i]);
} else {
dfs(i, d+1, x);
low[x] = min(low[x], low[i]);
if(low[i] > dep[x]) {
cout << i+1 << " " << x+1 << '\n';
}
}
}
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int n, e, a, b;
cin >> n >> e;
for(int i = 0; i < n; i++) {
p1[i] = p2[i] = i, sz1[i] = sz2[i] = 1;
}
for(int i = 0; i < e; i++) {
cin >> a >> b;
a--; b--;
if(root1(a) != root1(b)) {
merge1(a, b);
adj[a].push_back(b);
adj[b].push_back(a);
} else if(root2(a) != root2(b)) {
merge2(a, b);
adj[a].push_back(b);
adj[b].push_back(a);
}
}
for(int i = 0; i < n; i++) {
if(!v[i]) dfs(i, 0, -1);
}
}
