from sys import stdin
input=lambda :stdin.readline()[:-1]

n,m=map(int,input().split())
edge=[[] for i in range(n)]
IN=[0]*n
OUT=[0]*n
for i in range(m):
  a,b=map(lambda x:int(x)-1,input().split())
  IN[a]+=1
  OUT[b]+=1
  edge[a].append(b)
  edge[b].append(a)

G=[]
seen=[0]*n
for i in range(n):
  if seen[i]:
    continue
  todo=[i]
  seen[i]=1
  res=0
  flag=False
  size=0
  while todo:
    v=todo.pop()
    size+=1
    if IN[v]>OUT[v]:
      flag=True
      res+=IN[v]-OUT[v]
    for u in edge[v]:
      if seen[u]==0:
        seen[u]=1
        todo.append(u)
  if size!=1 or IN[i]!=0:
    G.append([res,flag])

  
ans=0
cnt1=0
cnt2=0
for x,y in G:
  ans+=x
  if y:
    cnt1=1
  else:
    cnt2+=1

if cnt2==0:
  print(ans-1)
else:
  print(ans+cnt2-1)