# include <cstdio>
# include <vector>
using namespace std;

FILE *f = freopen("ctc.in", "r", stdin);
FILE *g = freopen("ctc.out", "w", stdout);

const int N_MAX = 100001;

vector <int> G[N_MAX];
vector <int> GT[N_MAX];
vector <int> ctc[N_MAX];

int n, m, total = 0;
bool viz[N_MAX];
int stiva[N_MAX], index;

void read()
{
    scanf("%d %d", &n, &m);

    for (int i=1; i<=m; i++)
    {
        int x, y;
        scanf("%d %d", &x, &y);

        G[x].push_back(y);
        GT[y].push_back(x);
    }
}

void dfs(int nod)
{
    viz[nod] = true;

    for (int i : G[nod])
    {
        if (!viz[i])
            dfs(i);
    }

    stiva[++index] = nod;
}

void dfst(int nod)
{
    viz[nod] = true;

    for (int i : GT[nod])
    {
        if (!viz[i])
            dfst(i);
    }

    ctc[total].push_back(nod);
}

void solve()
{
    index = 0;

    for (int i=1; i<=n; i++)
        if (!viz[i])
            dfs(i);

    for (int i=1; i<=n; i++)
        viz[i] = false;

    for (int i=n; i>=1; i--)
    {
        if (!viz[stiva[i]])
        {
            total ++;
            dfst(stiva[i]);
        }
    }
}

void write()
{
    printf("%d\n", total);

    for(int i=1; i<=total; i++)
    {
        for(int j : ctc[i])
                printf("%d ", j);

        printf("\n");
    }
}

int main()
{
    read();
    solve();
    write();
    return 0;
}