#include <bits/stdc++.h>

using namespace std;

const int maxn = 100000, maxm = 200000;

int N, M;
vector <int> v[maxn + 1], inv[maxn + 1];
vector <int> topo;
vector <int> sol[maxn + 1];
int ans;
bool viz[maxn + 1];

void dfs_sort_top(int nod)  {
    if(viz[nod])
        return;
    viz[nod] = 1;
    for(auto &x : v[nod])  {
        dfs_sort_top(x);
    }
    topo.push_back(nod);
}

void dfsinv(int nod)  {
    if(!viz[nod])
        return;
    viz[nod] = 0;
    for(auto &x : inv[nod])  {
        dfsinv(x);
    }
    sol[ans].push_back(nod);
}

int main()  {
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    cin >> N >> M;
    for(int i = 0;i < M;i++)  {
        int x, y;
        cin >> x >> y;
        v[x].push_back(y);
        inv[y].push_back(x);
    }
    for(int i = 1;i <= N;i++)
        dfs_sort_top(i);
    for(int i = topo.size() - 1;i >= 0;i--)  {
        if(viz[topo[i]])  {
            dfsinv(topo[i]);
            ans++;
        }
    }
    cout << ans << "\n";
    for(unsigned int i = 0;i < ans;i++)  {
        for(auto &x : sol[i])
            cout << x << " ";
        cout << "\n";
    }
    return 0;
}