#include <fstream>
#include <vector>
#include <bitset>
#include <queue>
#include <algorithm>
#include <utility>
#include <cstring>
#include <string>
#include <stack>
#include <deque>
#include <iomanip>
#include <set>
#include <map>
#include <cassert>
#include <ctime>
#include <list>
#include <iomanip>

using namespace std;

string file = "ctc";

ifstream cin( (file + ".in").c_str() );
ofstream cout( (file + ".out").c_str() );

const int MAXN = 100005;
const int oo = (1<<31)-1;

typedef vector<int> Graph[MAXN];
typedef vector<int> :: iterator It;

const inline int min(const int &a, const int &b) { if( a > b ) return b;   return a; }
const inline int max(const int &a, const int &b) { if( a < b ) return b;   return a; }
const inline void Get_min(int &a, const int b)    { if( a > b ) a = b; }
const inline void Get_max(int &a, const int b)    { if( a < b ) a = b; }

struct ClassComp {
    inline bool operator () (const int &a, const int &b) const {
        return a > b;
    }
};

Graph G;
int N, M, Level[MAXN], LowLink[MAXN], deep;
set<set<int> > SCC;
stack<int> Stack;
bitset<MAXN> inStack;

inline void Tarjan(int Node) {
    Level[Node] = LowLink[Node] = ++ deep;
    Stack.push(Node);
    inStack[Node] = true;
    for(It it = G[Node].begin(), fin = G[Node].end() ; it != fin ; ++ it) {
        if(!Level[*it]) {
            Tarjan(*it);
            Get_min(LowLink[Node], LowLink[*it]);
        }
        else if(inStack[*it])
            Get_min(LowLink[Node], LowLink[*it]);
    }
    if(LowLink[Node] == Level[Node]) {
        set<int>actSCC;
        int node;
        do {
            actSCC.insert(node = Stack.top());
            Stack.pop();
            inStack[node] = false;
        }while(node != Node);
        SCC.insert(actSCC);
    }
}

int main() {
    cin >> N >> M;
    for(int i = 1 ; i <= M ; ++ i) {
        int x, y;
        cin >> x >> y;
        G[x].push_back(y);
    }
    for(int i = 1 ; i <= N ; ++ i)
        if(!Level[i])
            Tarjan(i);
    cout << SCC.size() << '\n';
    for(set<set<int> > :: iterator it = SCC.begin(), fin = SCC.end() ; it != fin ; ++ it, cout << '\n')
        for(set<int>::iterator itt = it->begin() , finn = it->end() ; itt != finn ; ++ itt)
            cout << *itt << ' ';
    cin.close();
    cout.close();
    return 0;
}