5
1 8 1 7 9
 4
6 7 4 5
 5
36 37 6 18 36
 3
5 1 3
 200
2 1 1 1 2 1 2 1 1 1 2 1 2 2 2 1 1 2 1 2 1 1 1 2 2 1 2 1 1 2 1 1 1 2 1 1 2 2 2 2 2 2 2 2 2 2 1 2 2 1 2 1 2 2 1 1 2 2 2 2 2 2 2 1 1 1 2 1 2 2 1 1 2 1 2 2 2 1 2 1 1 1 2 1 1 2 2 1 2 2 1 2 2 1 1 2 1 1 1 1 1 2 2 1 1 2 1 2 2 2 1 2 1 1 1 2 2 1 2 2 2 1 1 2 1 2 2 1 2 2 2 1 1 2 2 1 2 1 1 2 2 1 2 1 2 1 2 2 2 1 1 2 2 1 1 2 1 1 1 2 2 2 1 2 2 2 1 2 1 1 1 1 2 1 2 1 2 1 1 1 2 2 2 1 2 1 1 2 2 1 1 1 1 1 2 2 2 1 2 2
 10
104105246720 52052623360 213207545282560 426415090565120 6354080 832841973760 26650943160320 6506577920 50832640 832841973760
 3
9 4 4
 10
3 3 3 3 3 3 3 3 3 3
 100
24 33 88 55 4 24 19 19 63 90 9 47 24 74 21 43 20 100 58 15 36 66 13 4 9 51 24 96 50 27 100 41 92 9 67 94 17 11 98 24 72 57 96 85 50 9 45 41 63 76 80 59 25 67 21 84 88 15 62 60 79 65 5 66 1 85 92 100 61 75 44 96 53 97 2 28 83 42 60 42 34 73 44 99 58 46 75 100 75 55 35 52 93 80 69 75 50 67 100 77
 200
1 2 1 2 2 1 2 2 2 1 1 1 2 2 1 2 2 1 2 1 1 2 1 2 1 2 2 1 2 2 1 2 1 2 1 2 1 2 2 1 1 1 1 2 1 1 2 2 1 2 1 1 2 2 2 1 2 1 1 1 1 1 1 1 2 1 2 2 2 2 2 2 1 1 1 2 2 2 2 2 1 2 1 2 1 2 2 2 1 1 1 1 2 1 1 1 2 2 1 2 1 1 1 2 2 1 1 2 1 2 1 2 1 1 1 2 2 2 1 1 1 2 2 2 1 2 1 2 2 1 2 2 2 1 1 1 1 1 2 2 2 2 2 2 1 1 1 2 1 1 1 1 2 1 2 2 2 2 1 2 2 1 1 1 1 1 2 1 2 2 2 2 1 1 1 2 1 2 1 2 1 1 2 1 1 2 1 2 1 1 1 1 2 1 2 1 1 1 2 2
 4
3 1 5 5
 200
2 2 3 2 1 2 1 2 6 1 6 2 6 1 2 6 5 1 3 6 2 2 4 4 5 5 3 2 2 3 4 2 1 2 2 5 3 6 3 4 5 5 2 2 2 4 6 6 4 4 5 6 6 1 6 6 5 5 6 3 6 2 2 4 1 5 5 5 5 4 2 6 1 2 1 2 2 3 5 5 5 1 5 4 2 1 3 2 5 5 6 4 2 5 2 5 2 2 2 4 3 5 2 2 1 2 1 6 4 3 2 3 6 1 5 5 4 1 2 2 5 3 1 3 6 2 6 4 3 3 1 3 3 5 2 1 3 4 6 4 3 6 3 4 3 1 3 4 6 3 4 1 5 3 5 4 2 1 6 1 6 5 4 6 6 2 3 6 5 2 6 4 5 1 2 5 4 1 5 2 5 5 4 3 1 6 3 2 5 2 2 3 3 1 1 3 6 6 6 2
 200
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

3
 3
 2
 1
 33
 8
 1
 0
 91
 30
 2
 122
 0

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;
int par[maxn], h[maxn], dp[maxn];
vector<int> adj[maxn];
bitset<maxn> mark;
void dfs(int v) {
  mark[v] = 1;
  dp[v] = h[v];
  for (int u : adj[v]) {
    if (!mark[u]) {
      par[u] = v;
      h[u] = h[v] + 1;
      dfs(u);
      dp[v] = min(dp[v], dp[u]);
    } else if (u != par[v]) {
      dp[v] = min(dp[v], h[u]);
    }
  }
  if (h[v] && dp[v] == h[v]) {
    cout << 0;
    exit(0);
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int v, u;
    cin >> v >> u;
    v--;
    u--;
    adj[v].push_back(u);
    adj[u].push_back(v);
  }
  dfs(0);
  for (int i = 0; i < n; i++) {
    for (int j : adj[i]) {
      if (i > j) continue;
      int v = i, u = j;
      if (h[v] > h[u]) swap(v, u);
      if (v == par[u])
        cout << v + 1 << ' ' << u + 1 << '\n';
      else
        cout << u + 1 << ' ' << v + 1 << '\n';
    }
  }
}
