import sys
if sys.platform =='ios':
	import clipboard
	a=clipboard.get()
	a = a.split('\n')
	text = '\n'.join(a)
	with open('input_file.txt','w') as f:
		f.write(text)
	sys.stdin = open('input_file.txt')
	
n,m = map(int,input().split())

G = [[]for i in range(n)]

for i in range(m):
	A,B = map(int,input().split())
	A,B = A-1,B-1
	G[B].append(A)
cnt = 0	
for i in G:
	if len(i) == 0:
		cnt += 1
		
print(cnt)