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

using namespace std;

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

vector<int> G[100005], GT[100005], CTC[100005];
int v[100005];
stack<int> st; 
int n, m, x, y, ctc;

void dfs(int nod) {
	v[nod] = 1;
    for(auto i : G[nod]) {
        if(v[i] == 0) {
        	dfs(i);
        }
    }
    st.push(nod);
}

void dfsT(int nod) { // dfs pt graful transpus
	v[nod] = 2;
	CTC[ctc].push_back(nod);
    for(auto i : GT[nod]) {
        if(v[i] == 1) {
        	dfsT(i);
        }
    }
}

void stiva() {
    for(int i = 1; i <= n; i++) {
        if(v[i] == 0) {
        	dfs(i);
        }
    }
    while(!st.empty()) {
    	int nod = st.top();
        if(v[nod] == 1) {
        	ctc++;
            dfsT(nod);
        }
        st.pop();
    }
}

int main() {
    fin >> n >> m;
    while(m > 0) {
    	fin >> x >> y;
        G[x].push_back(y);
        GT[y].push_back(x);
        m--;
    }
    stiva();
    fout << ctc << "\n";
    for(int i = 1; i <= ctc; i++) {
        for(auto it : CTC[i]) {
            fout << it << " ";
        }
        fout << "\n";
    }
	return 0;
}