/// Tarjan 
#include <bits/stdc++.h>

using namespace std;

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

int n, m, st[100005], top, scc, nr;
vector <int> a[100005], ctc[100005];
int lowlink[100005], id[100005];
bitset <100005> onStack, viz;

void Dfs(int x)
{
    //cout << x << " ";
    viz[x] = 1;
    st[++top] = x;
    onStack[x] = 1;
    id[x] = lowlink[x] = ++nr;
    for (auto w : a[x])
    {
        if (viz[w] == 0)
            Dfs(w);
        if (onStack[w] == 1) lowlink[x] = min(lowlink[w], lowlink[x]);
    }

    if (id[x] == lowlink[x])
    {
        scc++; 
        while (top > 0 and st[top] != x)
        {
            ctc[scc].push_back(st[top]);
            onStack[st[top]] = 0;
            lowlink[st[top]] = x;
            top--;
        }
        ctc[scc].push_back(x);
        top--;
    }
}

void Test_Case()
{
    int i, x, y;
    fin >> n >> m;
    for (i = 1; i <= m; i++)
    {
        fin >> x >> y;
        a[x].push_back(y);
    }

    for (i = 1; i <= n; i++)
        if (viz[i] == 0)
            Dfs(i);

    fout << scc << "\n";
    for (i = 1; i <= scc; i++)
    {
        for (auto j : ctc[i])
            fout << j << " ";
        fout << "\n";
    }
    
}

int main()
{
    int t;
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    t = 1;
    while (t--)
        Test_Case();

    return 0;
}