#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;

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


int n, m, lastIndex, ctc;
vector<vector<int>> graph, ans;
vector <int> index, lowlink, current;
vector <bool> visited, inStack;
stack <int> stk;

void init() {
    graph = vector<vector<int>> (n + 1);
    index = vector <int> (n + 1);
    lowlink = vector <int> (n + 1);
    visited = vector <bool> (n + 1);
    inStack = vector <bool> (n + 1);
}


void read() {
    fin >> n >> m;
    init();
    int x, y;
    for(int i = 1; i <= m; i ++) {
        fin >> x >> y;
        graph[x].push_back(y);
    }
}

void tarjan(int node) {
    visited[node] = true;
    inStack[node] = true;
    stk.push(node);
    index[node] = lowlink[node] = ++lastIndex;
    for(const auto& neighbour : graph[node]) {

        if(!visited[neighbour]) {
            tarjan(neighbour);
            lowlink[node] = min(lowlink[node], lowlink[neighbour]);
        } else if(inStack[neighbour]) {
            lowlink[node] = min(lowlink[node], index[neighbour]);
        }
    }

    if(lowlink[node] == index[node]) {
        ++ctc;
        int stackNode;
        current.clear();
        do {
            stackNode = stk.top();
            inStack[stackNode] = false;
            stk.pop();
            current.push_back(stackNode);
        } while(stackNode != node);
        ans.push_back(current);
    }

}

void solve() {
    for(int i = 1; i <= n; i ++)
        if(!visited[i])
            tarjan(i);
}

void print() {
    fout << ctc << '\n';
    for(int i = 0; i < ctc; i ++, fout << '\n')
        for(const auto& node : ans[i])
            fout << node << " ";

}

int main() {
    read();
    solve();
    print();
}