#include <bits/stdc++.h>
using namespace std;
const int infInt = 1e9;
vector<int> adj[200010];
int parent[200010], low[200010], vis[200010];
bool bridge = false;
int _count = 1;
void dfs(int u) {
  vis[u] = low[u] = _count++;
  for (auto v : adj[u]) {
    if (!vis[v]) {
      parent[v] = u;
      dfs(v);
      low[u] = min(low[u], low[v]);
      if (low[v] > vis[u]) bridge = true;
    } else if (parent[u] != v)
      low[u] = min(low[u], vis[v]);
  }
}
int Vis[200010];
int Parent[200010];
set<pair<int, int>> Set;
void dfs_tree(int u) {
  Vis[u] = 1;
  for (auto v : adj[u]) {
    if (!Vis[v]) {
      Parent[v] = u;
      Set.insert(make_pair(u, v));
      dfs_tree(v);
    } else if (Parent[u] != v and Vis[v] == 1) {
      Set.insert(make_pair(u, v));
    }
  }
  Vis[u] = 2;
}
vector<pair<int, int>> edges;
int main() {
  cin.sync_with_stdio(0);
  cin.tie(0);
  int numEdges, numNodes;
  cin >> numNodes >> numEdges;
  for (int i = 0; i < numEdges; i++) {
    int u, v;
    cin >> u >> v;
    adj[u].push_back(v);
    adj[v].push_back(u);
    edges.push_back(make_pair(u, v));
  }
  dfs(1);
  if (bridge) {
    cout << 0 << "\n";
    return 0;
  }
  dfs_tree(1);
  for (int i = 0; i < edges.size(); i++) {
    int u = edges[i].first;
    int v = edges[i].second;
    if (Set.find(make_pair(u, v)) != Set.end()) {
      cout << u << " " << v << "\n";
    } else {
      cout << v << " " << u << "\n";
    }
  }
  return 0;
}
