#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <bits/stdc++.h>

#define MATA 100005

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

vector<int>graph[100005];
vector<int>cc[100005];
stack<int>myStack;
int N, M, x, y, ID, id[100005], lowlink[100005], ccNum;
bitset<MATA> onStack;

void tarjanDFS(int thisNode){
    id[thisNode] = lowlink[thisNode] = ++ID;
    myStack.push(thisNode);
    onStack[thisNode] = true;

    for(auto nextNode: graph[thisNode]){
        if(!id[nextNode]){
            tarjanDFS(nextNode);
            lowlink[thisNode] = min(lowlink[thisNode], lowlink[nextNode]);
        }
        else if(onStack[nextNode])
            lowlink[thisNode] = min(lowlink[thisNode], lowlink[nextNode]);

    }

    if(id[thisNode] == lowlink[thisNode]){
        ccNum++;
        int z;
        do{
            z = myStack.top(); myStack.pop();
            //lowlink[myStack.top()] = id[thisNode];
            cc[ccNum].push_back(z);
            onStack[z] = false;
        } while(z != thisNode);
    }
}

int main()
{
    fin >> N >> M;
    for(int i = 1; i <= M; i++){
        fin >> x >> y;
        graph[x].push_back(y);
    }

    for(int i = 1; i <= N; i++){
        if(!id[i])
            tarjanDFS(i);
    }

    fout << ccNum << endl;
    for(int i = 1; i <= ccNum; i++){
        for(auto x: cc[i])
            fout << x << ' ';
        fout << endl;
    }

    return 0;
}