N,M=map(int,input().split())
par=[i for i in range(N)]
E=[0]*N;F=[0]*N
rank=[0]*(N)
friend=[0]*N
block=[0]*N
size=[1]*N
def find(x):
  if par[x]==x:
    return x
  else:
    par[x]=find(par[x])
    return par[x]
 
#同じ集合か判定
def same(x,y):
  return find(x)==find(y)
 
def union(x,y):
  x=find(x)
  y=find(y)
  if x==y:
    return 
  if rank[x]>rank[y]:
    par[y]=x
    size[x]+=size[y]
  else:
    par[x]=y
    size[y]+=size[x]
    if rank[x]==rank[y]:
      rank[y]+=1
 
A=[]
for i in range(M):
  a,b=map(int,input().split())
  a-=1; b-=1
  E[a]+=1;F[b]+=1
  A.append((a,b))
  union(a,b)

D={}
for i in range(N):
  d=find(i)
  if d not in D:
    D[d]=[]
  D[d].append(i)
ans=0
for d in D:
  p,q=0,0
  for i in D[d]:
    if E[i]>F[i]:
      p+=E[i]-F[i]
    else:
      q+=F[i]-E[i]
  if p>1:
    ans+=p-1
G={} 
for a,b in A:
  d=find(a)
  if d not in G:
    G[d]=1
print(ans+len(G)-1)