#include <bits/stdc++.h>
using namespace std;
const int N = 1e5+5;
vector<int> adj[N];
int tin[N], par[N][2], low[N];
int get1(int src)
{
if(src == par[src][0]) return src;
return par[src][0] = get1(par[src][0]);
}
bool join1(int u, int v)
{
u = get1(u), v = get1(v);
if(u == v) return false;
par[u][0] = v;
return true;
}
int get2(int src)
{
if(src == par[src][1]) return src;
return par[src][1] = get2(par[src][1]);
}
bool join2(int u, int v)
{
u = get2(u), v = get2(v);
if(u == v) return false;
par[u][1] = v;
return true;
}
int n, m, tmp, u, v;
void dfs(int src, int pa = -1)
{
bool a = 0;
tin[src] = low[src] = ++tmp;
for(auto it : adj[src])
{
if(it == pa && !a)
{
a = 1;
continue;
}
if(tin[it])
{
low[src] = min(low[src], tin[it]);
continue;
}
dfs(it, src);
low[src] = min(low[src], low[it]);
if(low[it] > tin[src])
{
cout << src << ' ' << it << '\n';
}
}
return ;
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> n >> m;
for(int i = 1; i <= n; i++) par[i][0] = par[i][1] = i;
int a = 0;
for(int i = 0; i < m; i++)
{
cin >> u >> v;
if(join1(u, v) || join2(u, v))
{
adj[u].push_back(v), adj[v].push_back(u);
a += 2;
}
}
assert(a <= n*10);
for(int i = 1; i <= n; i++)
{
if(!tin[i]) dfs(i);
}
return 0;
}
