#include <fstream>
#include <vector>
#include <stack>
#include <bitset>

using namespace std;

int n, m, x, y, K;
bitset<100003> v;
vector<int> a[100003], inv[100003], w[100003];
stack<int> st;

ifstream F("ctc.in");
ofstream G("ctc.out");

void dfs(int x)
{
    v[x] = 1;
    vector<int> :: iterator it;
    for( it = a[x].begin(); it != a[x].end(); ++ it )
        if(!v[*it]) dfs(*it);
    st.push(x);
}

void dfs1(int nod)
{
    v[nod] = 1;
    vector<int> :: iterator it;
    for( it = inv[nod].begin(); it != inv[nod].end(); ++ it )
        if(!v[*it]) dfs1(*it);
    w[K].push_back(nod);
}

int main()
{
    F >> n >> m;
    for( int i = 1; i <= m; ++ i )
    {
        F >> x >> y;
        a[x].push_back(y);
        inv[y].push_back(x);
    }
    for( int i = 1; i <= n; ++ i )
        if(!v[i]) dfs(i);
    v = 0;
    while(!st.empty())
    {
        x = st.top();
        st.pop();
        if(!v[x])
        {
            K++;
            dfs1(x);
        }
    }
    G << K << '\n';
    vector<int> :: iterator it;
    for(int i = 1; i <= K; ++ i, G << '\n')
        for( it = w[i].begin(); it != w[i].end(); ++ it )
            G << *it << " ";
    return 0;
}