#include <bits/stdc++.h>

using namespace std;

const int len = 200005;
int n, m, x, y, cnt;
vector<int> g[len], gt[len], sol[len], v;
bitset<len> seen1, seen2;

void dfs1(int node) {
    seen1[node] = true;
    for (auto& next : g[node])
        if (!seen1[next])
            dfs1(next);
    v.push_back(node);
}

void dfs2(int node) {
    seen2[node] = true;
    for (auto& next : gt[node])
        if (!seen2[next])
            dfs2(next);
    sol[cnt].push_back(node);
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);

    cin >> n >> m;
    for (int i = 1; i <= m; i++) {
        cin >> x >> y;
        g[x].push_back(y);
        gt[y].push_back(x);
    }

    for (int i = 1; i <= n; i++)
        if (!seen1[i])
            dfs1(i);

    reverse(v.begin(), v.end());
    for (auto& it : v) {
        if (!seen2[it]) {
            cnt++;
            dfs2(it);
        }
    }

    cout << cnt << "\n";
    for (int i = 1; i <= cnt; i++) {
        for (auto& it : sol[i])
            cout << it << " ";
        cout << "\n";
    }
}