#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

using namespace std;

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

vector<bool> v;
vector< vector<int> > g, gt;
stack<int> st;
int n, m, q, cnt;

void dfs(int na)
{
    v[na] = 1;
    for (int i = 0; i < g[na].size(); ++ i)
        if (v[g[na][i]] == 0)
            dfs(g[na][i]);

    st.push(na);
}

void dfst(int na)
{
    v[na] = 0;
    for (int i = 0; i < gt[na].size(); ++ i)
        if (v[gt[na][i]] == 1)
            dfst(gt[na][i]);

   g[cnt].push_back(na);
}

void read()
{
    fin >> n >> m;
    g.resize(n + 1);
    gt.resize(n + 1);
    v.resize(n + 1);

    int x, y;
    for (int i = 1; i <= m; ++ i)
    {
        fin >> x >> y;
        g[x].push_back(y);
        gt[y].push_back(x);
    }
}

int main()
{
    read();
    for (int i = 1; i <= n; ++ i)
        if (v[i] == 0) dfs(i);

    while(!st.empty())
    {
        if(v[st.top()])
        {
            q = 0;
            cnt ++;
            g[cnt].resize(0);
            dfst(st.top());
        }
        st.pop();
    }

    fout << cnt;
    for (int i = 1; i <= cnt; ++ i)
    {
        fout <<'\n';
        for (int j = 0; j < g[i].size(); ++ j)
            fout << g[i][j] <<' ';
    }
    return 0;
}