#include <bits/stdc++.h>

using namespace std;
ifstream in("int.in");
ofstream out("int.out");
int n,m,nr=0;
short ap[100005],negru[100005];
vector <int> graf[100005];
vector <int> graf_transpus[100005];
vector <int> sol[100005];
deque <int> q;
void dfs_alb(int node)
{
    ap[node]=1;
    for(int i=0; i<graf[node].size(); i++)
    {
        if(!ap[graf[node][i]])
            dfs_alb(graf[node][i]);
    }
    q.push_front(node);
}
void dfs_negru(int node)
{
    ap[node]=0;
    for(int i=0; i<graf_transpus[node].size(); i++)
    {
        if(ap[graf_transpus[node][i]])
            dfs_negru(graf_transpus[node][i]);
    }
    sol[nr].push_back(node);
}
void solve()
{
    for(int i=1; i<=n; i++)
    {
        if(!ap[i])
        {
            dfs_alb(i);
        }
    }
    while(!q.empty())
    {
        if(ap[q.front()])
        {
            nr++;
            dfs_negru(q.front());
        }
        q.pop_front();
    }
}
int main()
{
    in >> n >> m;
    for(int i=1; i<=m; i++)
    {
        int x,y;
        in >> x >> y;
        graf[x].push_back(y);
        graf_transpus[y].push_back(x);
    }
    solve();
    out << nr << '\n';
    for(int i=1; i<=nr; i++)
    {
        for(int j=0; j<sol[i].size(); j++)
        {
            out << sol[i][j] << ' ';
        }
        out << '\n';
    }
    return 0;
}