#include <bits/stdc++.h>

typedef long long ll;
typedef long double ld;

using namespace std;

#define rep(i, a, n) for (int i = (a); i < (n); i++)
#define per(i, a, n) for (int i = (n) - 1; i >= (a); i--)

int N;
vector<vector<int>> Gfull;
vector<vector<int>> g;
vector<int> SCC;
stack<int> S;
vector<int> cislo, najmenej;
vector<bool>spracuvam;
int cas, nSCC;

void hladaj(int v) {
	cislo[v] = najmenej[v] = cas++;
	S.push(v); spracuvam[v] = true;
	for (int i = 0; i<int(Gfull[v].size()); i++){
		int kam = Gfull[v][i];
		if (cislo[kam] == -1) {hladaj(kam); najmenej[v] = min(najmenej[v], najmenej[kam]); }
		else if (spracuvam[kam]) najmenej[v] = min(najmenej[v], najmenej[kam]);
	}

	if (najmenej[v] == cislo[v]) {
		while (1) { int k = S.top(); S.pop(); spracuvam[k] = false; SCC[k] = nSCC; if (k == v) break; }
		nSCC++;
	}
}

int main(void) {
	ios::sync_with_stdio(false);
	int n, m;
	while (cin >> n >> m) {
		Gfull = {}; Gfull.resize(n);
		SCC = {}; SCC.resize(n, -1);
		cislo = {}; cislo.resize(n, -1);
		najmenej = {}; najmenej.resize(n, -1);
		spracuvam = {}; spracuvam.resize(n, false);
		while (!S.empty()) S.pop();
		cas = nSCC = 0;
		rep(i, 0, m) {
			int a, b;
			cin >> a >> b;
			a--, b--;
			Gfull[a].push_back(b);;
		}

		rep(i, 0, n)
			if (SCC[i] == -1) hladaj(i);

		vector<int> repr(nSCC);
		rep(i, 0, n)
			repr[SCC[i]] = i;

		g = {}; g.resize(nSCC);
		vector<unordered_set<int> > gset(nSCC);
		rep(i, 0, n)
			for (auto a : Gfull[i])
				if (SCC[i] != SCC[a])
					gset[SCC[i]].insert(SCC[a]);

		/*****************************/
		n = nSCC;

		rep(i, 0, n) for (auto a : gset[i]) g[i].push_back(a);
		vector<int> in, out;
		vector<bool> isout(n, true);
		rep(i,0,n) {
            if(g[i].size() == 0) {
                in.push_back(i);
            }
            for(auto x : g[i]) {
                isout[x] = false;
            }
		}
		rep(i,0,n) {
            if(isout[i]) out.push_back(i);
		}
        random_shuffle(in.begin(), in.end());
        random_shuffle(out.begin(), out.end());
        cout << max(in.size(), out.size()) << endl;
        rep(i,0,max(in.size(), out.size())) {
            cout << (repr[in[i%in.size()]]+1) << " " << (repr[out[i%out.size()]]+1) << endl;
        }
	}

	return 0;
}