#include <bits/stdc++.h>
using namespace std;

#ifdef DEBUG
ifstream in_file("minta/be2.txt");
#define input in_file
#define INTHENAMEOFGOD
#else
#define input cin
#define INTHENAMEOFGOD \
    ios::sync_with_stdio(0); \
    cin.tie(0); \
    cout.tie(0);
#endif
typedef long long ll;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<bool> vb;
typedef pair<ll, ll> pii;

ll N, M, a, b, visszacsat, kezdet;
vvi G;
vector<pii> kor;
vector<char> vis;
bool found;

void dfs1(ll x) {
    vis[x] = 1;
    for (ll next : G[x]) {
        if (!vis[next]) {
            dfs1(next);
            if (found) {
                kor[x] = {next, 0};
                return;
            }
        }
        if (vis[next] == 1) {
            kor[x] = {next, 0};
            visszacsat = next;
            found = true;
            return;
        }
    }
    vis[x] = 2;
}

void korbejar(ll tol, ll ig) {
    ll most = tol;
    while (most != ig) {
        kor[most].second++;
        most = kor[most].first;
    }
}

void dfs2(ll x) {
    vis[x] = 1;
    for (ll next : G[x]) {
        if (kor[next].first != -1 && next != kor[x].first) {
            korbejar(next, kezdet);
            continue;
        }
        if (kor[next].first == -1 && !vis[next]) {
            dfs2(next);
        }
    }
}

int main() {
    input >> N >> M;
    G.resize(N);
    for (ll m = 0; m < M; m++) {
        input >> a >> b;
        a--; b--;
        G[a].push_back(b);
    }

    kor.assign(N, {-1, -1});
    vis.assign(N, 0);
    for (ll i = 0; !found; i++) {
        assert(i < N);
        dfs1(i);
    }

    vis.assign(N, 0);
    for (ll n = 0; n < N; n++) {
        if (kor[n].first != -1) {
            kezdet = n;
            dfs2(n);
        }
    }

    ll maxfok = max_element(kor.begin(), kor.end(), [](pii a, pii b) {
        return a.second < b.second;
    })->second;

    ostringstream os("");
    ll db = 0;

    for (ll n = 0; n < N; n++) {
        if (kor[n].first != -1 && kor[n].second == maxfok) {
            db++;
            os << n+1 << " " << kor[n].first+1 << "\n";
        }
    }
    cout << db << "\n" << os.str() << endl;
}