#include <bits/stdc++.h>
using namespace std;
int main(){
  int N, M;
  cin >> N >> M;
  vector<vector<int>> E(N), E2(N);
  for (int i = 0; i < M; i++){
    int U, V;
    cin >> U >> V;
    U--;
    V--;
    E[U].push_back(V);
    E2[U].push_back(V);
    E2[V].push_back(U);
  }
  vector<int> d(N, 0);
  for (int i = 0; i < N; i++){
    for (int j : E[i]){
      d[j]++;
    }
  }
  queue<int> Q;
  for (int i = 0; i < N; i++){
    if (d[i] == 0){
      Q.push(i);
    }
  }
  vector<int> t;
  while (!Q.empty()){
    int v = Q.front();
    Q.pop();
    t.push_back(v);
    for (int w : E[v]){
      d[w]--;
      if (d[w] == 0){
        Q.push(w);
      }
    }
  }
  int cnt = t.size();
  vector<int> pos(N, -1);
  for (int i = 0; i < cnt; i++){
    pos[t[i]] = i;
  }
  int K = 0;
  vector<int> A, B;
  vector<bool> used(N, false);
  for (int i = 0; i < N; i++){
    if (!used[i]){
      used[i] = true;
      vector<int> id;
      queue<int> Q2;
      Q2.push(i);
      while (!Q2.empty()){
        int v = Q2.front();
        Q2.pop();
        id.push_back(v);
        for (int w : E2[v]){
          if (!used[w]){
            used[w] = true;
            Q2.push(w);
          }
        }
      }
      int cnt2 = id.size();
      if (cnt2 > 1){
        bool s = false;
        for (int j = 0; j < cnt2; j++){
          if (pos[id[j]] == -1){
            s = true;
          }
        }
        if (!s){
          vector<pair<int, int>> P(cnt2);
          for (int j = 0; j < cnt2; j++){
            P[j] = make_pair(pos[id[j]], id[j]);
          }
          sort(P.begin(), P.end());
          for (int j = 0; j < cnt2 - 1; j++){
            K++;
            A.push_back(P[j].second);
            B.push_back(P[j + 1].second);
          }
        } else {
          for (int j = 0; j < cnt2; j++){
            int j2 = j + 1;
            if (j2 == cnt2){
              j2--;
            }
            K++;
            A.push_back(id[j]);
            B.push_back(id[j2]);
          }
        }
      }
    }
  }
  cout << K << endl;
  for (int i = 0; i < K; i++){
    cout << A[i] + 1 << ' ' << B[i] + 1 << endl;
  }
}