# Uses python3

import sys

sys.setrecursionlimit(200000)


def explore(v, adj, visited, postV, clock):
    visited[v] = True
    for w in adj[v]:
        if visited[w] == False:
            explore(w, adj, visited, postV, clock)
    postV[v] = clock[0]
    clock[0] = clock[0] + 1


def reverseG(adj):
    adjReverse = [[] for _ in range(len(adj))]
    for v in range(len(adj)):
        for w in adj[v]:
            adjReverse[w].append(v)

    return adjReverse


def dfs(adj, visited, postV, clock):
    for v in range(len(adj)):
        if visited[v] == False:
            explore(v, adj, visited, postV, clock)


def exploreWithoutPostV(v, adj, visited):
    visited[v] = True
    for w in adj[v]:
        if visited[w] == False:
            exploreWithoutPostV(w, adj, visited)


def number_of_strongly_connected_components(adj):
    adjReversal = reverseG(adj)
    adjReversalVisited = [False] * len(adj)
    postV = [0] * len(adj)
    clock = [0]

    dfs(adjReversal, adjReversalVisited, postV, clock)
    temp = sorted(range(len(postV)), key=lambda k: postV[k], reverse=True)

    visited = [False] * len(adj)
    result = 0
    for i in temp:
        if visited[i] == False:
            exploreWithoutPostV(i, adj, visited)
            result = result + 1
    return result


if __name__ == '__main__':
    input = sys.stdin.read()
    data = list(map(int, input.split()))
    n, m = data[0:2]
    data = data[2:]
    edges = list(zip(data[0:(2 * m):2], data[1:(2 * m):2]))
    adj = [[] for _ in range(n)]
    for (a, b) in edges:
        adj[a - 1].append(b - 1)
    print(number_of_strongly_connected_components(adj))