from collections import *
import heapq
import bisect
import itertools


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 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())


INF = float("inf")
MOD = 998244353
mod = 998244353

N, M = map(int, input().split())
indeg = [0] * N
outdeg = [0] * N
uf = UnionFind(N)
for _ in range(M):
    u, v = map(int, input().split())
    u -= 1
    v -= 1
    uf.union(u, v)
    indeg[v] += 1
    outdeg[u] += 1
group = uf.roots()
ans = 0
for g in group:
    cnt = 0
    ok = False
    for member in uf.members(g):
        cnt += abs(indeg[member] - outdeg[member])
        if outdeg[member] > 0:
            ok = True
    if not ok:
        continue
    cnt //= 2
    ans += max(cnt - 1, 0) + 1
print(ans - 1)