#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
using namespace std;

vector<int> v[200009];
vector<pair<int, int> > r[200009], ans;
int id[200009], ds[200009], p[200009];
queue<int> q;

int uf(int n)
{
	if (ds[n] == n) return n;
	return ds[n] = uf(ds[n]);
}

int main()
{ 
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n, m; cin >> n >> m;
	for (int i = 1; i <= n; i++)
		ds[i] = i;
	for (int i = 0; i < m; i++) {
		int a, b; cin >> a >> b;
		v[a].push_back(b); 
		id[b]++;
		int ua = uf(a), ub = uf(b);
		if (ua != ub) ds[ua] = ub;
	}
	for (int i = 1; i <= n; i++) 
		if (!id[i])
			q.push(i);
	int c = 0;
	while (!q.empty()) {
		int hn = q.front(); q.pop();
		c++; p[hn] = c;
		for (int i = 0; i < v[hn].size(); i++) {
			int tn = v[hn][i];
			id[tn]--;
			if (!id[tn]) q.push(tn);
		}
	}
	for (int i = 1; i <= n; i++)
		r[uf(i)].push_back(make_pair(p[i], i));
	for (int i = 1; i <= n; i++) {
		if (ds[i] != i) continue;
		sort(r[i].begin(), r[i].end());
		for (int j = 0; j + 1 < r[i].size(); j++)
			ans.push_back(make_pair(r[i][j].second, r[i][j + 1].second));
		if (!r[i][0].first)
			ans.push_back(make_pair(r[i].back().second, r[i][0].second));
	}
	cout << ans.size() << '\n';
	for (int i = 0; i < ans.size(); i++)
		cout << ans[i].first << " " << ans[i].second << '\n';
	return 0;
}