# またWA出た
# outward-inwardだと輪っかを0としてしまう
# UFも組み合わせて、数えていなければカウント増やそう

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 unite(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 all_group_members(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 '\n'.join(f'{r}: {m}' for r, m in self.all_group_members().items())


N, M = map(int, input().split())
UF = UnionFind(N+1)
inward = [0]*(N+1)
outward = [0]*(N+1)
for i in range(M):
    u, v = map(int, input().split())
    outward[u] += 1
    inward[v] += 1
    UF.unite(u, v)

count = 0
visited = set()
for i in range(1, N+1):
    if outward[i]-inward[i] > 0:
        count += outward[i]-inward[i]
        root = UF.find(i)
        visited.add(root)
        
for i in range(1, N+1):
    if outward[i] > 0:
        root = UF.find(i)
        if root not in visited:
            visited.add(root)
            count += 1
        
ans = count-1
print(ans)