#include <iostream>
#include <fstream>
#include <vector>
#include <unordered_set>
#include <stack>
#define siz 100003
using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");
int lowlink[ siz ],deepth[ siz ],x,y,n,m,nrct = 0,l=1;
unordered_set < int > se[siz];
bool visited[ siz],in_stack[siz];
vector < int > v [ siz ];
stack < int > st;
void dfs(int i)
{
    int j;
    for(auto it = v[i].begin(); it !=v[i].end(); it++)
    {
        j = *it;
        if(!visited[j])
        {
            deepth[j] = lowlink[j] = ++l;
            in_stack[j] = true;
            st.push(j);
            visited[j] = true;
            dfs(j);
            lowlink[i] = min(lowlink[i],lowlink[j]);
        }
        else
            if(in_stack[j])
                lowlink[i] = min(lowlink[i],lowlink[j]);
    }
    if( deepth[i] == lowlink[i] )
    {
        while(st.top()!=i)
        {
            se[nrct].insert(st.top());
            in_stack[st.top()] = false;
            st.pop();
        }
        se[nrct].insert(st.top());
        in_stack[st.top()]= false;
        st.pop();
        nrct++;
    }
}
int main()
{
    int i;
    in >> n >> m;
    for( i = 0 ; i < m ; i ++)
    {
        in >> x >> y;
        v[x].push_back(y);
    }
    for( i = 1 ; i <= n ; i ++)
    {
        deepth[i] = -1;
        visited[i] = false;
        in_stack[i] = false;
    }
    for( i = 1 ; i <= n ; i++)
        if (deepth[i] == -1)
        {
            deepth[i] = lowlink[i] = ++l;
            in_stack[i] = true;
            st.push(i);
            visited[i] = true;
            dfs(i);
        }
    out << nrct << "\n";
    for( i = 0 ; i < nrct ; i ++)
    {
        for( auto it = se[i].begin(); it != se[i].end() ; it ++)
            out << *it << " ";
        out << "\n" ;
    }
    return 0;
}