#include<cstdio>
#include<vector>
#define MAX_N 100000
using namespace std;

vector<int> L[MAX_N+1], G[MAX_N+1], v[MAX_N+1];
int f[MAX_N], n, m, k, nrctc;
bool used[MAX_N+1];

void Read()
{
    int i, x, y;
    FILE *fin = fopen("ctc.in","r");
    fscanf(fin,"%d%d",&n,&m);
    for(i=1; i<=m; i++)
    {
        fscanf(fin,"%d%d",&x,&y);
        L[x].push_back(y);
        G[y].push_back(x);
    }
    fclose(fin);
}

void DFS(int x)
{
    used[x] = true;
    for(vector<int>::iterator it = L[x].begin(); it != L[x].end(); it++)
        if(!used[(*it)])
            DFS(*it);
    f[k++] = x;
}

void DFSreverseGraph(int x)
{
    used[x] = true;
    v[nrctc].push_back(x);
    for(vector<int>::iterator it = G[x].begin(); it != G[x].end(); it++)
        if(!used[(*it)])
            DFSreverseGraph(*it);
}

int main()
{
    vector<int>::iterator it;
    int i;
    FILE *fout = fopen("ctc.out","w");
    Read();
    for(i=1; i<=n; i++)
        if(!used[i])
            DFS(i);
    for(i=1; i<=n; i++)
        used[i] = false;

    for(i=k-1; i>=0; i--)
        if(!used[f[i]])
        {
            DFSreverseGraph(f[i]);
            nrctc++;
        }
    fprintf(fout,"%d\n",nrctc);
    for(i=0; i<nrctc; i++)
    {
        for(it = v[i].begin(); it != v[i].end(); it++)
            fprintf(fout,"%d ",*it);
        fprintf(fout,"\n");
    }
    fclose(fout);
    return 0;
}