Problem:


Score : 100 points

Problem Statement

You are given a directed graph with N vertices and M edges, not necessarily simple. The i-th edge is oriented from the vertex a_i to the vertex b_i.
Divide this graph into strongly connected components and print them in their topological order.

Constraints

1 \leq N \leq 500,000

1 \leq M \leq 500,000

0 \leq a_i, b_i < N

Input

Input is given from Standard Input in the following format:

N M
a_0 b_0
a_1 b_1
:
a_{M - 1} b_{M - 1}

Output

Print 1+K lines, where K is the number of strongly connected components.
Print K on the first line. 
Print the information of each strongly connected component in next K lines in the following format, where l is the number of vertices in the strongly connected component and v_i is the index of the vertex in it.

l v_0 v_1 ... v_{l-1}

Here, for each edge (a_i, b_i), b_i should not appear in earlier line than a_i.

If there are multiple correct output, print any of them.

Sample Input 1

6 7
1 4
5 2
3 0
5 5
4 1
0 3
4 2

Sample Output 1

4
1 5
2 4 1
1 2
2 3 0



Sample input:
6 7
1 4
5 2
3 0
5 5
4 1
0 3
4 2


Sample output:
4
1 5
2 4 1
1 2
2 3 0

Submission status: Accepted

Solution code:
code = r"""
# distutils: language=c++
# distutils: include_dirs=[/home/contestant/.local/lib/python3.8/site-packages/numpy/core/include, /opt/atcoder-stl]
from libcpp.vector cimport vector
cdef extern from "<atcoder/scc>" namespace "atcoder" nogil:
    cdef cppclass scc_graph:
        scc_graph(int n)
        void add_edge(int fr, int to)
        vector[vector[int]] scc()
from libc.stdio cimport getchar, printf
cdef inline int read():
    cdef int b, c = 0
    while 1:
        b = getchar() - 48
        if b < 0: return c
        c = c * 10 + b
cdef int n = read(), m = read(), a, b, i, j
cdef scc_graph *g = new scc_graph(n)
for i in range(m):
    a = read()
    b = read()
    g.add_edge(a, b)
cdef vector[vector[int]] res = g.scc()
m = res.size()
printf('%d', m)
for i in range(m):
    m = res[i].size()
    printf('\n%d', m)
    for j in range(m): printf(' %d', res[i][j])
"""
import os, sys
if sys.argv[-1] == 'ONLINE_JUDGE':
    open('solve.pyx', 'w').write(code)
    os.system('cythonize -i -3 -b solve.pyx')
import solve