#include <iostream>
#include <stack>
#include <string.h>
#include <vector>
#include <queue>
#include <map>

using namespace std;

typedef vector <vector<int>> Graph;

vector<int> tsort(Graph G, int start, int end) {
  vector<int> ret;

  int degree[end];
  memset(degree, 0, sizeof(degree));

  for (int from = start; from < end; from++) {
    for (int i = 0; i < G[from].size(); i++) {
      int to = G[from][i];
      degree[to]++;
    }
  }

  stack<int> root;

  for (int i = start; i < end; i++) {
    if (degree[i] == 0) {
      root.push(i);
    }
  }

  while (!root.empty()) {
    int from = root.top();
    root.pop();

    ret.push_back(from);

    for (int i = 0; i < G[from].size(); i++) {
      int to = G[from][i];
      degree[to]--;

      if (degree[to] == 0) {
        root.push(to);
      }
    }
  }

  return ret;
}

int main() {
  int N, M;
  cin >> N >> M;

  Graph OG(N);
  Graph DG(N);

  int u, v;

  for (int i = 0; i < M; ++i) {
    cin >> u >> v;
    --u;
    --v;

    DG[u].push_back(v);
    OG[u].push_back(v);
    OG[v].push_back(u);
  }

  bool checked[N];
  memset(checked, false, sizeof(checked));
  vector<int> U;
  vector<int> V;

  for (int v = 0; v < N; ++v) {
    if (checked[v]) continue;

    queue<int> que;
    que.push(v);
    int id = 0;
    map<int, int> mapping;
    map<int, int> r_mapping;
    vector<int> vs;

    while (not que.empty()) {
      int x = que.front();
      que.pop();

      if (checked[x]) continue;
      checked[x] = true;
      mapping[x] = id;
      r_mapping[id] = x;
      id++;
      vs.push_back(x);

      for (int u : OG[x]) {
        if (checked[u]) continue;
        que.push(u);
      }
    }

    int n = vs.size();
    if (n >= 2) {
      fprintf(stderr, "n: %d\n", n);
      Graph G(n);
      for (int x : vs) {
        int from = mapping[x];

        for (int u : DG[x]) {
          int to = mapping[u];
          G[from].push_back(to);
        }
      }

      vector<int> res = tsort(G, 0, n);
      int k = res.size() - 1;
      for (int i = 0; i < k; ++i) {
        int a = res[i];
        int b = res[i + 1];
        a = r_mapping[a];
        b = r_mapping[b];
        U.push_back(a);
        V.push_back(b);
      }
    }
  }

  int K = U.size();
  cout << K << endl;
  for (int i = 0; i < K; ++i) {
    cout << U[i] + 1 << " " << V[i] + 1 << endl;
  }

  return 0;
}