#include <bits/stdc++.h>
using namespace std;

int n, m, tsort[100005], k, x, y;
vector <int> v[100005], inv[100005], sol[100005];
bool u[100005];

void dfs(int q){
    u[q] = 1;
    for (auto it: v[q])
        if (!u[it]) dfs(it);
    tsort[++k] = q;
}

void dfsinv(int q){
    u[q] = 0;
    for (auto it: inv[q])
        if (u[it]) dfsinv(it);
    sol[x].push_back(q);
}

int main(){
    ifstream cin ("ctc.in");
    ofstream cout ("ctc.out");
    cin >> n >> m;
    for (int i=1; i<=m; i++){
        cin >> x >> y;
        v[x].push_back(y);
        inv[y].push_back(x);
    }
    for (int i=1; i<=n; i++){
        if (!u[i]) dfs(i);
    }
    x = 0;
    for (int i=n; i; i--)
        if (u[tsort[i]]) x++, dfsinv(tsort[i]);
    cout << x << "\n";
    for (int i=1; i<=x; i++){
        for (auto it: sol[i]) cout << it << " ";
        cout << "\n";
    }
    return 0;
}