N, K = map(int, input().split())
g0 = [[] for _ in range(N+1)]
g1 = [[] for _ in range(N+1)]
for _ in range(K):
    a, b = map(int, input().split())
    g0[a].append(b)
    g1[b].append(a)

ans = 0
seen = [0]*(N+1)
ct0 = ct1 = 0
for i in range(1, N+1):
    if seen[i]:
        continue
    seen[i] = 1
    task = [i]
    flag = 0
    for v in task:
        for u in g0[v]:
            flag = 1
            if seen[u]:
                continue
            seen[u] = 1
            task.append(u)
        for u in g1[v]:
            flag = 1
            if seen[u]:
                continue
            seen[u] = 1
            task.append(u)
    if not flag:
        continue
    res = sum(abs(len(g0[v])-len(g1[v])) for v in task)//2
    if res:
        ct1 += 1
        ans += res-1
    else:
        ct0 += 1
ans += max(0, ct0+ct1-1)
print(ans)