#include <bits/stdc++.h>
using namespace std;
vector<vector<long long> > g, res;
vector<vector<long long> > d;
vector<long long> used;
vector<long long> pr;
vector<long long> sum;
vector<long long> gl;
void dfs(long long v, long long p, long long glb) {
  gl[v] = glb;
  pr[v] = p;
  used[v] = 1;
  for (long long to : g[v])
    if (!used[to])
      dfs(to, v, glb + 1), d[v].push_back(to), res[v].push_back(to);
}
void dfs_sum(long long v, long long p) {
  for (long long to : d[v])
    if (to != p) dfs_sum(to, v), sum[v] += sum[to];
}
void solve() {
  long long n, m;
  cin >> n >> m;
  g.resize(n);
  vector<pair<long long, long long> > e(m);
  for (long long i = 0; i < m; ++i) {
    long long a, b;
    cin >> a >> b, a--, b--;
    g[a].push_back(b);
    g[b].push_back(a);
    e[i] = {a, b};
  }
  used.resize(n);
  pr.resize(n);
  d.resize(n);
  res.resize(n);
  sum.resize(n);
  gl.resize(n);
  dfs(0, 0, 0);
  for (long long i = 0; i < m; ++i) {
    long long a = e[i].first;
    long long b = e[i].second;
    if (gl[a] < gl[b]) swap(a, b);
    if (gl[a] != gl[b] + 1) {
      res[a].push_back(b);
      sum[a]++;
      sum[b]--;
    }
  }
  dfs_sum(0, 0);
  for (long long i = 1; i < n; ++i)
    if (!sum[i]) {
      cout << 0;
      return;
    }
  for (long long i = 0; i < n; ++i)
    for (long long to : res[i]) cout << i + 1 << " " << to + 1 << "\n";
}
int32_t main() {
  ios_base::sync_with_stdio(NULL);
  cin.tie(0);
  cout.tie(0);
  long long t = 1;
  while (t--) solve();
}
