#include <stdio.h>

#define NMAX 100000
#define MMAX 200000

static struct edge {
    int vertex;
    int next;
} edges[2*MMAX+1];

static int adj[NMAX+1], adj_t[NMAX+1], done[2*NMAX+1], output[2*NMAX+1], t, nout;
static char visited[NMAX+1];

static void dfs(int s, char is_first_dfs)
{
    int e;

    visited[s] = is_first_dfs;

    for (e = is_first_dfs ? adj[s] : adj_t[s]; e != 0; e = edges[e].next) {
        if (visited[edges[e].vertex] != is_first_dfs) {
            dfs(edges[e].vertex, is_first_dfs);
        }
    }

    if (is_first_dfs) {
        done[t++] = s;
    } else {
        output[++nout] = s;
    }
}

int main(void)
{
    int i, n, m, u, v;

    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);

    scanf("%d %d", &n, &m);

    for (i = 1; i <= m; i++) {
        scanf("%d %d", &u, &v);

        edges[2*i].vertex = v;
        edges[2*i].next = adj[u];
        adj[u] = 2*i;

        edges[2*i+1].vertex = u;
        edges[2*i+1].next = adj_t[v];
        adj_t[v] = 2*i+1;
    }

    for (i = 1; i <= n; i++) {
        if (visited[i] == 0) {
            dfs(i, 1);
        }
    }

    while (t--) {
        if (visited[done[t]] == 1) {
            dfs(done[t], 0);
            output[++nout] = -1;
            output[0]++;
        }
    }

    printf("%d\n", output[0]);

    for (m = i = 0; i < output[0]; i++) {
        while (output[++m] != -1) {
            printf("%d ", output[m]);
        }

        printf("\n");
    }

    return 0;
}