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

using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");
vector <int> a[100005], scc[100005];
int n, m, st[100005], top, id[100005], lowlink[100005], nr, nrscc;
bitset <100005> onStack;

void Dfs(int x)
{
    st[++top] = x;
    onStack[x] = 1;
    id[x] = lowlink[x] = ++nr;

    for (auto w : a[x])
    {
        if (id[w] == 0)
            Dfs(w);
        if (onStack[w]) lowlink[x] = min(lowlink[w], lowlink[x]);
    }

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

int main()
{
    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 (id[i] == 0)
        Dfs(i);

    fout << nrscc << "\n";
    for (i = 1; i <= nrscc; i++)
    {
        for (auto j : scc[i])
            fout << j << " ";
        fout << "\n";
    }
    return 0;
}