#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> pi;
#define dep par1
#define low par2
int n, m, a, b, co, par1[100001], par2[100001];
vector<int> adj[100001];
inline int __attribute__((optimize("Ofast"), target("arch=sandybridge"))) read_int() {
int x = 0;
char ch = getchar_unlocked();
while (ch < '0' || ch > '9') ch = getchar_unlocked();
while (ch >= '0' && ch <= '9'){
x = (x << 3) + (x << 1) + ch - '0';
ch = getchar_unlocked();
}
return x;
}
int __attribute__((optimize("Ofast"), target("arch=sandybridge"))) root(int *array, int x){
if(array[x] == -1) return x;
return array[x] = root(array, array[x]);
}
void __attribute__((optimize("Ofast"), target("arch=sandybridge"))) connect(int *array, int x, int y){
array[root(array, x)] = root(array, y);
adj[x].push_back(y);
adj[y].push_back(x);
}
void __attribute__((optimize("Ofast"), target("arch=sandybridge"))) bridges(int x, int par){
if(dep[x] != -1) return;
dep[x] = low[x] = co++;
int t = 0;
for(auto it:adj[x]){
if(it == par && t == 0){ t++; continue; }
if(dep[it] != -1){
if(low[it] > dep[x]) cout << x << " " << it << "\n";
low[x] = min(low[x], low[it]);
continue;
}
bridges(it, x);
if(low[it] > dep[x]) cout << x << " " << it << "\n";
low[x] = min(low[x], low[it]);
}
}
int __attribute__((optimize("Ofast"), target("arch=sandybridge"))) main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
memset(par1, -1, sizeof(par1));
memset(par2, -1, sizeof(par2));
n = read_int(); m = read_int();
for(int i = 0; i < m; i++){
a = read_int(); b = read_int();
if(a > b) swap(a, b);
if(root(par1, a) != root(par1, b)) connect(par1, a, b);
else if(root(par2, a) != root(par2, b)) connect(par2, a, b);
}
memset(par1, -1, sizeof(par1));
memset(par2, -1, sizeof(par2));
for(int i = 1; i <= n; i++) bridges(i, 0);
}
