#include <bits/stdc++.h>

using namespace std;

FILE *F=fopen("ctc.in", "r"), *G=fopen("ctc.out", "w");

int x, y, n, m, k, K, w[100005];
bitset<100005> v;
vector<int> a[100005], a1[100005], V[200005];

void dfs(int nod)
{
    vector<int> :: iterator it;
    v[nod] = 1;
    for(it = a[nod].begin(); it != a[nod].end(); ++ it)
        if(!v[*it]) dfs(*it);
    w[++k] = nod;
}

void dfs1(int nod)
{
    vector<int> :: iterator it;
    v[nod] = 1;
    for(it = a1[nod].begin(); it != a1[nod].end(); ++ it)
        if(!v[*it]) dfs1(*it);
    V[K].push_back(nod);
}

int main()
{
    fscanf(F, "%d %d ", &n, &m);
    for(int i = 1; i <= m; ++ i)
    {
        fscanf(F, "%d %d ", &x, &y);
        a[x].push_back(y);
        a1[y].push_back(x);
    }
    for(int i = 1; i <= n; ++ i)
        if(!v[i]) dfs(i);
    v = 0;
    vector<int> :: iterator it;
    for(int i = k; i > 0; -- i)
        if(!v[w[i]]) ++ K, dfs1(w[i]);
    fprintf(G, "%d\n", K);
    for(int i = 1; i <= K; ++ i, fputc('\n', G))
        for(it = V[i].begin(); it != V[i].end(); ++ it)
            fprintf(G, "%d ", *it);
    return 0;
}