N,M = map(int,input().split())
Gnum = [0] * (N + 1)

for _ in range(M):
    u,v = map(int,input().split())
    Gnum[u] -= 1
    Gnum[v] += 1
    
a = 0
b = 0
p = 0
q = 0
for i in range(1,N + 1):
    if Gnum[i] == 1:
        if a == 0:a = 1
        else:
            p += 1
    elif Gnum[i] == -1:
        if b == 0:b = 1
        else:
            q += 1
    elif Gnum[i] == 0:
        pass
    elif Gnum[i] > 0:
        p += Gnum[i]
    else:
        q -= Gnum[i]
print(p)