from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline




N,M = map(int,input().split())
ind = [0]*N
for _ in range(M):
    a,b = map(int,input().split())
    a -= 1
    b -= 1
    ind[b] += 1

print(sum(ind[i]==0 for i in range(N)))