#include<bits/stdc++.h>
#define INF 2e9
using namespace std;

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

vector <int> h[100003];
vector <int> g[100003];
vector <int> scc[100003];

int n,m, nrc;
int viz[100003], st[100003], top;

void DFS(int n)
{
    viz[n]=1;
    for(int i:h[n])
        if (viz[i] == 0)
            DFS(i);
    st[++top]=n;
}

void DFS2 (int n)
{
    viz[n]=0;
    for(int i:g[n])
        if(viz[i] ==1)
            DFS2(i);
    scc[nrc].push_back(n);
}

void SCC ()
{
    for(int i=1; i<=n; i++)
        if (viz[i]==0)
            DFS(i);

    for (int i=n; i>0; i--)
    {
        if(viz[st[i]]==1)
        {
            nrc++;
            DFS2(st[i]);
        }
    }
}

void Afis()
{
    fout<<nrc<<endl;
    for(int i=1; i<=nrc; i++)
    {
        for(int j:scc[i])
            fout<<j<<" ";
        fout<<endl;
    }
}

int main()
{
    fin>>n>>m;
    for(int i=1; i<=m; i++)
    {
        int x,y;
        fin>>x>>y;
        h[x].push_back(y);
        g[y].push_back(x);
    }

    SCC();
    Afis();
    return 0;
}