Егору прикол

import sys

sys.setrecursionlimit(100000)

num_v = int(input())
num_e = int(input())

graph = []
t_graph = []

used = [0] * num_v
order = []
component = []

pairs = []

for i in range(num_v):
    graph.append([])
    t_graph.append([])

for i in range(num_e):
    edge = list(map(int, input().split()))
    start_v = edge[0] - 1
    end_v = edge[1] - 1

    pairs.append([start_v, end_v])
    graph[start_v].append(end_v)
    t_graph[end_v].append(start_v)


def dfs_1(v=int):
    used[v] = 1
    for i in graph[v]:
        if used[i] == 0:
            dfs_1(i)
    order.append(v)


def dfs_2(v=int):
    used[v] = 1
    component.append(v)
    for i in t_graph[v]:
        if used[i] == 0:
            dfs_2(i)


for i in range(num_v):
    if used[i] == 0:
        dfs_1(i)

used = [0] * num_v

v_component = [0] * num_v
n = 0
for i in range(num_v):
    v = order[num_v - 1 - i]
    if used[v] == 0:
        dfs_2(v)
        for j in component:
            v_component[j] = n
        n += 1
        component.clear()

b_stations = [0] * n
for i in range(num_e):
    if v_component[pairs[i][0]] != v_component[pairs[i][1]]:
        b_stations[v_component[pairs[i][0]]] = 1

stations = []
for i in range(n):
    if b_stations[i] == 0:
        for j in range(num_v):
            if v_component[j] == i:
                stations.append(j + 1)
                break

print(len(stations))
print(*stations, sep=' ')