#include <bits/stdc++.h>
/*
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#pragma GCC target ("avx2")
*/
using namespace std;
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template<class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
*/
#define F first
#define S second
#define pb push_back
#define md(a) ((a%mod+mod)%mod)
#define all(a) a.begin(), a.end()
#define MP make_pair
#define lc (id<<1)
#define rc (lc|1)
#define mid (l+r)/2
#define kill(a) cout << a << "\n", exit(0)
#define SZ(a) (ll)a.size()
typedef pair<int,int> pii;
typedef pair<long long ,long long> pll;
typedef long long ll;
typedef long double ld;
typedef vector<vector<ll>> matrix;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll const maxn=1e5+10, mod=1e9+7, INF=1e18, LOG=31, sq=65;
ll poww(ll a, ll b, ll mod) {
if (b == 0) return 1;
return 1 * poww(1 * a * a % mod, b / 2, mod) * ((b % 2 == 1) ? a : 1) % mod;
}
int n, m, par0[maxn], par1[maxn], sz0[maxn], sz1[maxn], h[maxn], low[maxn];
vector<pii> g[maxn];
void DSU()
{
for(int i=0;i<maxn;i++) {
par0[i]=par1[i]=i;
sz0[i]=sz1[i]=1;
}
}
int Find0(int v) {return par0[v]==v?v:par0[v]=Find0(par0[v]);}
int Find1(int v) {return par1[v]==v?v:par1[v]=Find1(par1[v]);}
bool Union(int v, int u)
{
int v0, u0;
if((v0=Find0(v))==(u0=Find0(u))){
int v1, u1;
if((v1=Find1(v))==(u1=Find1(u))) return 0;
if(sz1[v1]<sz1[u1]) swap(v1, u1);
par1[u1]=v1;
sz1[v1]+=sz1[u1];
return 1;
}
if(sz0[v0]<sz0[u0]) swap(v0, u0);
par0[u0]=v0;
sz0[v0]+=sz0[u0];
return 1;
}
void DFS(int v, int p=0, int lst=0)
{
h[v]=h[p]+1;
low[v]=h[v];
for(auto [u, id]:g[v])
{
if(id==lst) continue;
if(!h[u]) DFS(u, v, id);
low[v]=min(low[v], low[u]);
}
if(low[v]==h[v] && p!=0)
{
cout<<v<<" "<<p<<"\n";
}
}
int main() {
cin>>n>>m;
DSU();
for(int i=1;i<=m;i++)
{
int v, u;
cin>>v>>u;
if(Union(v, u)){
g[v].pb({u, i});
g[u].pb({v, i});
}
}
for(int i=1;i<=n;i++)
{
if(!h[i]) DFS(i);
}
return 0;
}
