n,m = map(int,input().split())
a = [0]*n; b = [0]*n; c = []
for _ in range(m):
    u,v = map(int,input().split())
    a[u-1] += 1; b[v-1] += 1
for u,v in zip(a,b):
    if u>v: c.append(u-v)
print(max(sum(c)-1,0))