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 = []; 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 = len(set(uf.f(i) for i in range(n)))-1
for u,v in zip(a,b):
    if u>v: c.append(u-v)
    if u==v==0: ans -= 1
print(ans+max(sum(c)-1,0))