n, m = map(int, input().split())
in_degree = [0] * (n + 1)

for _ in range(m):
    a, b = map(int, input().split())
    in_degree[b] += 1

count = 0
for i in range(1, n + 1):
    if in_degree[i] == 0:
        count += 1

print(count)