def root(x):
  p=x
  l=[p]
  while r[p]!=p:
    p=r[p]
    l+=[p]
  for p in l:
    r[p]=l[-1]
  return r[x]

def union(x,y):
  rx=root(x)
  ry=root(y)
  if rx==ry:
    return
  if rx>ry:
    rx,ry=ry,rx
  r[ry]=rx
  v[rx]+=v[ry]
  v[ry]=[]
  return

n,m=map(int,input().split())
r=list(range(n))
v=[[i] for i in range(n)]
d=[0]*n
for i in range(m):
  a,b=map(int,input().split())
  a-=1
  b-=1
  d[a]+=1
  d[b]-=1
  union(a,b)
c1=0
c2=0

for l in v:
  if len(l)<=1:
    continue
  c2+=1
  c=sum(abs(d[i]) for i in l)
  c//=2
  if c<=1:
    continue
  c1+=c-1

print(c1+c2-1)