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

using namespace std;

ifstream in("ctc.in");
ofstream out("ctc.out");
int n, m, x, y, time, nr;
vector<int>l[100002],t[100002], color(100002),sol[100002];
stack<pair<int,int> >st;

void dfs(int k){
    color[k] = 1;
    for(vector<int>::const_iterator it = l[k].begin(); it != l[k].end(); it++){
        x = *it;
        if(color[x] == 0) dfs(x);
    }
    color[k] = 2; time = time + 1;
    st.push(make_pair(k,time));
}

void dfst(int k){
    color[k] = 1;
    sol[nr].push_back(k);
    for(vector<int>::const_iterator it = t[k].begin(); it != t[k].end(); it++){
        if(color[*it] == 0) dfst(*it);
    }
    color[k] = 2;
}
int main()
{
    in >> n >> m;
    for(int i = 1; i <= m; i++){
        in >> x >> y;
        l[x].push_back(y);t[y].push_back(x);
    }

    for(int i = 1; i <= n; i++){
        if(color[i] == 0) dfs(i);
    }

    for(int i = 1; i <= n; i++) color[i] = 0;
    while(!st.empty()){
        x = st.top().first; y = st.top().second;
        st.pop();
        //cout << x << ": " << y << "\n";
        if(color[x] == 0) {
                nr = nr + 1; dfst(x);
        }
    }
    out << nr << "\n";
    for(int i = 1; i <= nr; i++){
        for(vector<int>::const_iterator it = sol[i].begin(); it != sol[i].end(); it++) out << *it << " ";
        out << "\n";
    }
    return 0;
}