#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define ld long double
#define ull unsigned long long
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<long long, long long>
#define vi vector<int>
#define vl vector<long long>
#define pb push_back
#define rep(i, b) for(int i = 0; i < (b); ++i)
#define rep2(i,a,b) for(int i = a; i <= (b); ++i)
#define rep3(i,a,b,c) for(int i = a; i <= (b); i+=c)
#define count_bits(x) __builtin_popcountll((x))
#define all(x) (x).begin(),(x).end()
#define siz(x) (int)(x).size()
#define forall(it,x) for(auto& it:(x))
using namespace __gnu_pbds;
using namespace std;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
//mt19937 mt;void random_start(){mt.seed(chrono::time_point_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()).time_since_epoch().count());}
//ll los(ll a, ll b) {return a + (mt() % (b-a+1));}
const int INF = 1e9+50;
const ll INF_L = 1e18+40;
const ll MOD = 1e9+7;
const int maxn = 100001;
int rep_[maxn];
int siz_[maxn];
int rep2[maxn];
int P[maxn];
vi sons[maxn];
int depth[maxn];
vector<pii> ans;
int fint_comp(int v)
{
if(rep2[v] == v) return v;
rep2[v] = fint_comp(rep2[v]);
return rep2[v];
}
int fint(int v)
{
if(rep_[v] == v) return v;
rep_[v] = fint(rep_[v]);
return rep_[v];
}
void onion(int a, int b)
{
a = fint(a);
b = fint(b);
if(a == b) return;
siz_[b] += siz_[a];
rep_[a] = b;
}
int nxt;
void dfs_upd(int v, int pop, int d)
{
depth[v] = d;
P[v] = pop;
rep(i,siz(sons[v]))
{
nxt = fint_comp(sons[v][i]);
if(nxt == v)
{
swap(sons[v][siz(sons[v])-1],sons[v][i]);
sons[v].pop_back();
i--;
continue;
}
if(nxt != pop)
{
dfs_upd(nxt,v,d+1);
}
}
}
void onion_comps(int a, int b)
{
a = fint_comp(a);
b = fint_comp(b);
if(siz(sons[a]) > siz(sons[b])) swap(a,b);
rep2[a] = b;
forall(it,sons[a])
{
sons[b].pb(it);
}
sons[a] = {};
}
void add_edge(int a, int b)
{
if(fint_comp(a) == fint_comp(b)) return;
if(fint(a) != fint(b))
{
ans.pb({a,b});
int ca = fint(a);
int cb = fint(b);
if(siz_[ca] > siz_[cb]) swap(a,b);
onion(a,b);
a = fint_comp(a);
b = fint_comp(b);
dfs_upd(a,b,depth[b]+1);
sons[a].pb(b);
sons[b].pb(a);
}
else
{
vi con;
a = fint_comp(a);
b = fint_comp(b);
while(a != b)
{
if(depth[a] > depth[b])
{
con.pb(a);
a = fint_comp(P[a]);
}
else
{
con.pb(b);
b = fint_comp(P[b]);
}
}
con.pb(a);
int p = P[a];
int d = depth[a];
rep(i,siz(con)-1)
{
onion_comps(con[i],con[i+1]);
}
P[fint_comp(a)] = p;
depth[fint_comp(a)] = d;
}
}
int main()
{
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//random_start();
int n,m;
cin >> n >> m;
rep2(i,1,n)
{
rep_[i] = i;
rep2[i] = i;
siz_[i] = 1;
depth[i] = 0;
P[i] = i;
}
rep(i,m)
{
int a,b;
cin >> a >> b;
add_edge(a,b);
}
forall(it,ans)
{
if(fint_comp(it.ff) != fint_comp(it.ss))
{
cout << it.ff << " " << it.ss << "\n";
}
}
}
