/* -*- coding: utf-8 -*-
 *
 * 1553.cc:  No.1553 Lovely City - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 200000;

/* typedef */

typedef vector<int> vi;
typedef queue<int> qi;
typedef pair<int,int> pii;

struct UFT {
  int links[MAX_N], ranks[MAX_N], sizes[MAX_N];
  UFT() {}

  void init(int n) {
    for (int i = 0; i < n; i++) links[i] = i, ranks[i] = sizes[i] = 1;
  }

  int root(int i) {
    int i0 = i;
    while (links[i0] != i0) i0 = links[i0];
    return (links[i] = i0);
  }

  int rank(int i) { return ranks[root(i)]; }
  int size(int i) { return sizes[root(i)]; }
  bool same(int i, int j) { return root(i) == root(j); }

  int merge(int i0, int i1) {
    int r0 = root(i0), r1 = root(i1), mr;
    if (r0 == r1) return r0;
    if (ranks[r0] == ranks[r1]) {
      links[r1] = r0;
      sizes[r0] += sizes[r1];
      ranks[r0]++;
      mr = r0;
    }
    else if (ranks[r0] > ranks[r1]) {
      links[r1] = r0;
      sizes[r0] += sizes[r1];
      mr = r0;
    }
    else {
      links[r0] = r1;
      sizes[r1] += sizes[r0];
      mr = r1;
    }
    return mr;
  }
};

/* global variables */

vi nbrs[MAX_N], vs[MAX_N];
int pns[MAX_N], ids[MAX_N], sv[MAX_N];
UFT uft;
pii es[MAX_N];

/* subroutines */

/* main */

int main() {
  int n, m;
  scanf("%d%d", &n, &m);

  uft.init(n);

  for (int i = 0; i < m; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    u--, v--;
    nbrs[u].push_back(v);
    pns[v]++;
    uft.merge(u, v);
  }

  memset(ids, -1, sizeof(ids));
  int gn = 0;

  for (int i = 0; i < n; i++) {
    int ri = uft.root(i);
    if (ids[ri] < 0) ids[ri] = gn++;
    vs[ids[ri]].push_back(i);
  }
  //printf("gn=%d\n", gn);

  int k = 0;
  for (int gi = 0; gi < gn; gi++) {
    vi &vg = vs[gi];

    qi q;
    for (auto u: vg)
      if (pns[u] == 0) q.push(u);

    int sn = 0;
    while (! q.empty()) {
      int u = q.front(); q.pop();
      sv[sn++] = u;

      for (auto v: nbrs[u])
	if (--pns[v] == 0) q.push(v);
    }

    if (sn == vg.size())
      for (int i = 0; i + 1 < sn; i++)
	es[k++] = pii(sv[i], sv[i + 1]);
    else {
      for (int i = 0; i + 1 < vg.size(); i++)
	es[k++] = pii(vg[i], vg[i + 1]);
      es[k++] = pii(vg[vg.size() - 1], vg[0]);
    }
  }

  printf("%d\n", k);
  for (int i = 0; i < k; i++)
    printf("%d %d\n", es[i].first + 1, es[i].second + 1);
  return 0;
}