import sys
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
inf = 2 ** 63 - 1
mod = 998244353

n, m = mi()
graph = [[] for _ in range(n)]

for _ in range(m):
    a, b = mi()
    a -= 1; b -= 1
    graph[b].append(a)
cnt = 0
for i in range(n):
    if len(graph[i]) == 0:
        cnt += 1
print(cnt)