#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
#define pb push_back
// #define int ll
const int maxn = 1e5 + 10;
int par1[maxn], par2[maxn], sz1[maxn], sz2[maxn];
int get1(int v) {
if (par1[v] == v)
return v;
else
return par1[v] = get1(par1[v]);
}
bool merge1(int v, int u) {
v = get1(v);
u = get1(u);
if (v == u)
return false;
if (sz1[v] < sz1[u])
swap(v, u);
sz1[v] += sz1[u];
par1[u] = v;
return true;
}
int get2(int v) {
if (par2[v] == v)
return v;
else
return par2[v] = get2(par2[v]);
}
bool merge2(int v, int u) {
v = get2(v);
u = get2(u);
if (v == u)
return false;
if (sz2[v] < sz2[u])
swap(v, u);
sz2[v] += sz2[u];
par2[u] = v;
return true;
}
int n, m, dep[maxn];
vector<int> G[maxn];
bool mark[maxn];
vector<pii> candi;
int dfs(int v, int p, int depth) {
mark[v] = 1;
dep[v] = depth;
int res = depth, cnt = 0;
for (int u : G[v]) {
if (u == p && cnt == 0) {
cnt++;
continue;
}
if (mark[u])
res = min(res, dep[u]);
else
res = min(res, dfs(u, v, depth + 1));
}
if (p != 0 && res == depth) {
candi.pb({p, v});
}
return res;
}
void cutEdge() {
for (int i = 1; i <= n; i++) {
if (!mark[i])
dfs(i, 0, 0);
}
for (auto [v, u] : candi)
cout << v << ' ' << u << '\n';
}
int main() {
ios_base::sync_with_stdio(false);cout.tie(0);cin.tie(0);
cin >> n >> m;
for (int i = 1; i <= n; i++) {
sz1[i] = sz2[i] = 1;
par1[i] = par2[i] = i;
}
for (int i = 1; i <= m; i++) {
int v, u;
cin >> v >> u;
if (get1(v) != get1(u)) {
merge1(v, u);
G[v].pb(u);
G[u].pb(v);
continue;
}
else if (get2(v) != get2(u)) {
merge2(v, u);
G[v].pb(u);
G[u].pb(v);
continue;
}
}
cutEdge();
}
