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

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

#define N 1000001

int n, m, id = 1, sccCnt = 0;
vector<int> a[N];
int ids[N], low[N], onStack[N];
stack<int> s;

void dfs(int x){
    s.push(x);
    onStack[x] = true;
    ids[x] = low[x] = id++;

    for(int k : a[x]){
        if(ids[k] == 0)
            dfs(k);
        if(onStack[k])
            low[x] = min(low[x], low[k]);
    }

    if(ids[x] == low[x]){
        while(s.empty() == false){
            int node = s.top();
            s.pop();
            onStack[node] = false;
            low[node] = ids[x];
            if(node == x) break;
        }
        sccCnt++;
    }
}

void findSCCs(){
    for(int i=1; i<=n; i++){
        if(ids[i] == 0)
            dfs(i);
    }

    out << sccCnt << '\n';

    set<int> keys;
    unordered_map<int, set<int>> m;

    for(int i=1; i<=n; i++){
        keys.insert(low[i]);
        m[low[i]].insert(i);
    }

    for(int i : keys){
        for(int k : m[i])
            out << k << ' ';
        out << '\n';
    }
}


int main(){
    in >> n >> m;
    while(m--){
        int x, y;
        in >> x >> y;
        a[x].push_back(y);
    }

    findSCCs();
}