n, m = map(int, input().split())
in_ = [0] * n
out_ = [0] * n

for _ in range(m):
    u, v = map(int, input().split())
    u -= 1
    v -= 1
    in_[v] += 1
    out_[u] += 1

tot = 0
for i, o in zip(in_, out_):
    tot += max(0, i - o)

print(max(0, tot - 1))