#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
const int MaxN = 4e5 + 10;
const int MAXN = 120 * 1000;
void fun() {}
long long phi(long long n) {
  long long result = n;
  for (long long p = 2; p * p <= n; ++p) {
    if (n % p == 0) {
      while (n % p == 0) n /= p;
      result -= result / p;
    }
  }
  if (n > 1) result -= result / n;
  return result;
}
long long mult(long long a, long long b, long long mod) {
  long long res = 0;
  a %= mod;
  while (b) {
    if (b & 1) res = (res + a) % mod;
    a = (2 * a) % mod;
    b >>= 1;
    return res;
  }
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long lcm(long long a, long long b) { return (a / gcd(a, b) * b); }
long long ncr(long long n, long long r) {
  long long res = 1;
  if (r > n) return 0;
  if (r > n - r) r = n - r;
  for (long long i = 0; i < r; i++) {
    res *= (n - i);
    res /= (i + 1);
  }
  return res;
}
vector<long long> factors(long long n) {
  vector<long long> f;
  for (long long x = 2; x * x <= n; x++) {
    if (n % x == 0) {
      f.push_back(x);
      if ((n / x) != x) f.push_back(n / x);
    }
  }
  return f;
}
int cD(long long n) { return floor(log10(n) + 1); }
long long powmod(long long a, long long b) {
  long long ans = 1;
  while (b) {
    if (b & 1) {
      ans = ans * a % mod;
    }
    a = a * a % mod;
    b >>= 1;
  }
  return ans;
}
long long inv(long long x) { return powmod(x, mod - 2); }
long long cat(long long n) {
  long long final = 1;
  for (int i = 0; i < n; i++) {
    final = final * (2 * n - i) % mod * inv(1 + i) % mod;
  }
  final = final * inv(1 + n) % mod;
  return final;
}
long long bin(long long x, long long y) {
  if (y == 0) {
    return 1;
  }
  long long u = bin(x, y / 2);
  if (y % 2 == 0) {
    return u * u % mod;
  } else {
    return u * u % mod * x % mod;
  }
}
long long modFact(long long n, long long mod) {
  if (n >= mod) return 0;
  long long result = 1;
  for (int i = 1; i <= n; i++) result = (result * i) % mod;
  return result;
}
double nthRoot(double n, int k) {
  return pow(k, (1.0 / k) * (log(n) / log(k)));
}
long long MAX = 1e6;
long long n, k, q, c, r, h;
long long l, t;
string s;
std::vector<int> adj[100001];
long long visited[100001];
long long chi[100001];
long long dist[100001];
long long timer;
long long in[100001];
long long low[100001];
long long d;
long long cc;
bool edge = false;
vector<pair<int, int>> el;
void dfs(int curr, int par) {
  visited[curr] = 1;
  low[curr] = in[curr] = timer++;
  for (int child : adj[curr]) {
    if (child == par) continue;
    if (visited[child]) {
      low[curr] = min(low[curr], in[child]);
      if (in[curr] > in[child]) el.push_back({curr, child});
    } else {
      dfs(child, curr);
      if (low[child] > in[curr]) {
        edge = true;
        return;
      }
      el.push_back({curr, child});
      low[curr] = min(low[curr], low[child]);
    }
  }
}
int main() {
  fun();
  ios_base::sync_with_stdio(false);
  long long n, m, e;
  long long t;
  cin >> n >> e;
  for (int i = 0; i < e; i++) {
    cin >> l >> r;
    adj[l].push_back(r);
    adj[r].push_back(l);
  }
  dfs(1, -1);
  if (edge == true) {
    cout << 0 << "\n";
  } else {
    for (int i = 0; i < el.size(); i++)
      cout << el[i].first << " " << el[i].second << "\n";
  }
  return 0;
}
