n,m=map(int,input().split())

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

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