from collections import defaultdict

class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def group(self):
        group_members = defaultdict(list)
        for member in range(self.n):
            group_members[self.find(member)].append(member)
        return group_members

    def __str__(self):
        return ''.join(f'{r}: {m}' for r, m in self.group().items())

n,m = map(int,input().split())
uf = UnionFind(n)
graph = [[] for i in range(n+1)]
e=[]
dout = defaultdict(int)
din = defaultdict(int)
for i in range(m):
    a,b = map(int,input().split())
    a -= 1
    b -= 1
    graph[a].append(b)
    e.append([a,b])
    uf.union(a,b)
    dout[b]+=1
    din[a]+=1

cnt1=defaultdict(list)
cnt2=-1

for i,l in uf.group().items():
    if len(l)==1:continue
    cnt2+=1
    for j in l:
        cnt1[i].append(abs(dout[j] - din[j]))

ans=0
for i,l in cnt1.items():
    le = len(l)
    s=sum(l)
    if s == 0:
        continue
    elif le == 2 and s == 2:
        ans += 1
    else:
        ans += s//2-1

print(ans+cnt2)