#include <bits/stdc++.h>
using namespace std;
const int MaxN = 120000;
const int MaxE = 620005;
struct Edge {
  int from, to;
  bool vst;
  Edge* next;
} memo[MaxE], *cur, *g[MaxN];
int vst[MaxN], n, m;
int p[MaxN], id[MaxN], low[MaxN];
int find(int x) {
  if (x != p[x])
    return p[x] = find(p[x]);
  else
    return x;
}
void init() {
  for (int i = 1; i <= n; i++) {
    g[i] = NULL;
    vst[i] = 0;
    p[i] = i;
  }
  cur = memo;
}
void add(int u, int v) {
  cur->from = u;
  cur->to = v;
  cur->vst = false;
  cur->next = g[u];
  g[u] = cur++;
}
bool dfs(int u, int fa, int K) {
  int v;
  vst[u] = 1;
  id[u] = low[u] = K;
  for (Edge* it = g[u]; it; it = it->next) {
    v = it->to;
    if (v != fa && vst[v] == 1) {
      if (id[u] > id[v]) {
        it->vst = true;
        low[u] = min(low[u], id[v]);
      }
    }
    if (vst[v] == 0) {
      if (!dfs(v, u, K + 1)) return false;
      low[u] = min(low[u], low[v]);
      it->vst = true;
      if (low[v] > id[u]) return false;
    }
  }
  vst[u] = -1;
  return true;
}
int main() {
  int u, v, cnt;
  while (scanf("%d%d", &n, &m) == 2) {
    init();
    while (m--) {
      scanf("%d%d", &u, &v);
      add(u, v);
      add(v, u);
      p[find(u)] = find(v);
    }
    cnt = 0;
    for (int i = 1; cnt < 2 && i <= n; i++)
      if (find(i) == i) cnt++;
    if (cnt == 1 && dfs(1, 0, 0)) {
      for (Edge* it = memo; it != cur; it++) {
        if (it->vst) {
          printf("%d %d\n", it->from, it->to);
        }
      }
    } else {
      puts("0");
    }
  }
  return 0;
}
