import sys
input = sys.stdin.readline

N, M = map(int, input().split())
S, T = [0] * N, [0] * N
for i in range(M):
    u, v = map(int, input().split())
    u, v = u - 1, v - 1
    S[u] += 1
    T[v] += 1
    
ans = 0
for i in range(N):
    ans += max(0, S[i] - T[i])
print(max(0, ans-1))