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

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

const int Max = 1e5 + 1;
int n, m, c;
vector<int> g[Max], t[Max], ctc[Max];
bitset<Max> v;
stack<int> s;

void dfs(int node)
{
    v[node] = 1;
    for(int i: g[node])
        if(!v[i])
            dfs(i);
    s.push(node);
}

void dfs2(int node)
{
    ctc[c].push_back(node);
    v[node] = 1;
    for(int i: t[node])
        if(!v[i])
            dfs2(i);
}

void kosaraju()
{
    for(int i = 1; i <= n; ++i)
        if(!v[i])
            dfs(i);
    v.reset();
    while(!s.empty())
    {
        if(!v[s.top()])
        {
            ++c;
            dfs2(s.top());
        }
        s.pop();
    }
}

int main()
{
    ios::sync_with_stdio(false);
    fin.tie(NULL);

    fin >> n >> m;
    for(int i = 1; i <= m; ++i)
    {
        int x, y;
        fin >> x >> y;
        g[x].push_back(y);
        t[y].push_back(x);
    }
    kosaraju();
    fout << c << "\n";
    for(int i = 1; i <= c; ++i, fout << "\n")
        for(int j: ctc[i])
            fout << j << " ";

    fin.close();
    fout.close();
    return 0;
}