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

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

int n, m, lastIndex, stronglyConnectedComponents;
vector <vector<int>>v, ctc;
vector <int> index, lowlink;
vector <bool> visited, inStack;
stack <int> stk;

void init() {
    v = 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);
    ctc.push_back({});
}

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

void tarjan(int node) {

    stk.push(node);
    visited[node] = true;
    inStack[node] = true;
    index[node] = lowlink[node] = ++lastIndex;

    for(const auto& neighbor : v[node]) {
        if(!visited[neighbor]) { ///tree edge
            tarjan(neighbor);
            lowlink[node] = min(lowlink[node], lowlink[neighbor]);
        }
        else if(inStack[neighbor]) { ///back edge
            lowlink[node] = min(lowlink[node], index[neighbor]);
        }
    }

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

void solve() {
    for(int i = 1; i <= n; i ++)
        if(!visited[i])
            tarjan(i);
        fout << stronglyConnectedComponents << '\n';
        for(int i = 1; i <= stronglyConnectedComponents; i ++, fout << '\n')
            for(const auto& node : ctc[i])
                fout << node << ' ';
}

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