#include <bits/stdc++.h>

using namespace std;

const int nmax = 1e5 + 10;

int n, m;
bool used[nmax];
vector < int > topo, now;
vector < int > g[nmax], gt[nmax];

vector < vector < int > > ans;

void dfs(int node) {
    used[node] = 1;
    for (auto &it: g[node]) {
        if (used[it]) continue;
        dfs(it);
    }

    topo.push_back(node);
}

void dfst(int node) {
    used[node] = 1; now.push_back(node);
    for (auto &it: gt[node]) {
        if (used[it]) continue;
        dfst(it);
    }
}

void run_scc() {
    for (int i = 1; i <= n; ++i)
        if (!used[i]) dfs(i);

    reverse(topo.begin(), topo.end());
    memset(used, 0, sizeof(used));

    for (auto &it: topo)
        if (!used[it]) {
            now.clear();
            dfst(it);
            ans.push_back(now);
        }
}

void output() {
    cout << ans.size() << '\n';
    for (int i = 0; i < ans.size(); ++i) {
        for (auto &it: ans[i])
            cout << it << ' ';
        cout << '\n';
    }
}

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

    ios_base :: sync_with_stdio(false);

    cin >> n >> m;
    for (int i = 1; i <= m; ++i) {
        int x, y;
        cin >> x >> y;

        g[x].push_back(y);
        gt[y].push_back(x);
    }

    run_scc();
    output();

    return 0;
}