#include <fstream>
#include <vector>
#include <cstring>

using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

const int DIM = 100001;

int n, m, x, y;
vector<int> d[DIM], t[DIM], sol[DIM];
vector<int> nodes;
int scc[DIM], sccCnt;
bool vis[DIM];

void dfs1(int node) {
    vis[node] = true;
    for (auto adjNode : d[node])
        if (!vis[adjNode])
            dfs1(adjNode);
    nodes.push_back(node);
}

void dfs2(int node) {
    vis[node] = true;
    sol[sccCnt].push_back(node);
    for (auto adjNode : t[node])
        if (!vis[adjNode])
            dfs2(adjNode);
}

int main() {
    fin >> n >> m;
    for (int i = 1; i <= m; i++) {
        fin >> x >> y;
        d[x].push_back(y);
        t[y].push_back(x);
    }

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

    sccCnt = 0;
    memset(vis, false, sizeof(vis));
    for (auto it = nodes.rbegin(); it != nodes.rend(); it++) {
        if (!vis[*it]) {
            sccCnt++;
            dfs2(*it);
        }
    }

    fout << sccCnt << '\n';
    for (int i = 1; i <= sccCnt; i++) {
        for (auto node : sol[i])
            fout << node << ' ';
        fout << '\n';
    }

    return 0;
}