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

char *p1, *p2, buf[1000000];
#define gc() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1000000,stdin),p1==p2)?EOF:*p1++)
inline int read() {int x=0;char c=gc();while(!isdigit(c))c=gc();while(isdigit(c))x=x*10+c-'0',c=gc();return x;}
#define pc(c) putchar(c)
void write(int x) {if(x>9)write(x/10);pc('0'+x%10);}

int n, m;
int head[500010], nxt[500010], to[500010], tot;
int dfn[500010], low[500010], dfst;
int stk[500010], vis[500010], top;
int scc[500010];
vector<vector<int>> sccs; int cnt;
int indeg[500010], a[500010];

inline void add_edge(int u, int v) {
    nxt[++tot] = head[u], to[tot] = v, head[u] = tot;
}

void dfs(int u) {
    dfn[u] = ++dfst, low[u] = u;
    stk[++top] = u, vis[u] = 1;
    for (int i = head[u]; i; i = nxt[i]) {
        int v = to[i];
        if (!dfn[v]) {
            dfs(v);
            low[u] = min(low[u], low[v]);
        } else if (vis[v]) {
            low[u] = min(low[u], dfn[v]);
        }
    }
    if (low[u] == u) {
        cnt++;
        sccs.emplace_back();
        int v;
        do {
            v = stk[top--];
            vis[v] = 0;
            sccs[cnt].push_back(v);
        } while (v != u);
    }
}

int main() {
    n = read(), m = read();
    for (int i = 1; i <= m; i++) {
        int u = read() + 1, v = read() + 1;
        add_edge(u, v);
    }
    sccs.emplace_back();
    for (int i = 1; i <= n; i++) {
        if (!dfn[i]) dfs(i);
    }
    for (int u = 1; u <= n; u++) {
        for (int i = head[u]; i; i = nxt[i]) {
            int v = to[i];
            indeg[scc[v]]++;
        }
    }
    queue<int> Q;
    for (int i = 1; i <= cnt; i++) {
        if (indeg[i] == 0) Q.push(i);
    }
    while (!Q.empty()) {
        a[++top] = Q.front();
        for (int u : sccs[Q.front()]) {
            for (int i = head[u]; i; i = nxt[i]) {
                int v = to[i];
                if (--indeg[v] == 0) Q.push(v);
            }
        }
        Q.pop();
    }
    write(cnt); pc('\n');
    for (int i = cnt; i >= 1; i--) {
        write(sccs[a[i]].size()); pc(' ');
        for (int u : sccs[a[i]]) write(u - 1), pc(' ');
        pc('\n');
    }
    return 0;
}