#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#define NMAX 100010
#define MIN(a, b) (  (a) < (b) ? (a) : (b) )

using namespace std;

vector<int> edges[NMAX];
vector<int> solValues[NMAX];
stack<int> sol;
int ind[NMAX], ll[NMAX], nr = 0, value, nrOfComp = 0;
bool visited[NMAX];

void dfs(int node) {
    visited[node] = 1;
    sol.push(node);
    ind[node] = ll[node] = ++nr;
    for(auto it:edges[node]) {
        if (!ind[it]) {
            dfs(it);
            ll[node] = MIN(ll[it], ll[node]);
        }
        else if(visited[it]) {
            ll[node] = MIN(ind[it], ll[node]);
        }
    }
    if (ll[node] == ind[node]) {
        while (!sol.empty()) {
            value = sol.top();
            sol.pop();
            visited[value] = 0;
            solValues[nrOfComp].push_back(value);
            if (value == node) {
                nrOfComp++;
                break;
            }
        }
    }
}

int main() {
    int n, m, x, y;
    ifstream fin("ctc.in");
    ofstream fout("ctc.out");
    fin >> n >> m;
    for (int i=1; i<=m; i++) {
        fin >> x >> y;
        edges[x].push_back(y);
    }
    for (int i=1; i<=n; i++) {
        if (!ind[i]) {
            dfs(i);
        }
    }
    fout << nrOfComp << "\n";
    for (int i=0; i<nrOfComp; i++) {
        for (auto it: solValues[i]) {
            fout << it << " ";
        }
        fout << "\n";
    }
    return 0;
}