N,M = map(int,input().split())
G = [[] for _ in range(N)]
for i in range(M):
    A,B = map(int,input().split())
    A-=1; B-=1;
    G[B].append(A)
    
cnt = 0
for i in G:
    if not i:
        cnt+=1
        
print(cnt)