n, m = map(int, input().split())
C = [0 for _ in range(n)]
for _ in range(m):
    u, v = map(int, input().split())
    u -= 1
    v -= 1
    C[u] -= 1
    C[v] += 1
ans = 0
for i in range(n):
    ans += max(C[i], 0)
print(ans - 1)