class UF:
    def __init__(self,n):
        self.p = [-1]*n
    def f(self,x):
        if self.p[x]<0: return x
        else: self.p[x] = self.f(self.p[x]); return self.p[x]
    def u(self,x,y):
        x = self.f(x); y = self.f(y)
        if x==y: return
        if -self.p[x]<-self.p[y]: x,y = y,x
        self.p[x] += self.p[y]; self.p[y] = x
n,m = map(int,input().split())
a = [0]*n; b = [0]*n; c = [[] for _ in range(n)]; uf = UF(n)
for _ in range(m):
    u,v = map(int,input().split())
    a[u-1] += 1; b[v-1] += 1; uf.u(u-1,v-1)
ans = 0
for i,(u,v) in enumerate(zip(a,b)):
    if u>v or u==v>0: c[uf.f(i)].append(u-v)
p = q = ans = 0
for i in range(n):
    if c[i]:
        p += 1; ans += sum(c[i])
        if sum(c[i])==0: q += 1
print(q-1 if p==q else max(ans-1,0)+q)