import sys
sys.setrecursionlimit(5*10**5)
input = sys.stdin.readline
from collections import defaultdict, deque, Counter
from heapq import heappop, heappush
from bisect import bisect_left, bisect_right
from math import gcd

from collections import defaultdict


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

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

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

    def same(self, a, b):
        return self.find(a) == self.find(b)

    def group(self):
        d = defaultdict(list)
        for i in range(1, self.n+1):
            par = self.find(i)
            d[par].append(i)
        return d


n,m = map(int,input().split())
graph = [[] for i in range(n+1)]
uf = UnionFind(n)
indeg = [0]*(n+1)
outdeg = [0]*(n+1)
for i in range(m):
    a,b = map(int,input().split())
    graph[a].append(b)
    uf.union(a,b)
    indeg[b] += 1
    outdeg[a] += 1

g = uf.group()

ans = 0
gg = 0
for k,v in g.items():
    cnt = 0
    tmp = 0
    for i in v:
        if indeg[i] >= outdeg[i]:
            cnt += indeg[i] - outdeg[i]
        tmp += indeg[i]
    ans += max(cnt-1, 0)
    gg += tmp >= 1

print(ans + gg-1)