mod = 1000000007
eps = 10**-9


def main():
    import sys
    from collections import deque
    input = sys.stdin.readline

    N, M = map(int, input().split())
    in_num = [0] * (N+1)
    out_num = [0] * (N+1)
    adj = [[] for _ in range(N+1)]
    for _ in range(M):
        a, b = map(int, input().split())
        adj[a].append(b)
        adj[b].append(a)
        in_num[b] += 1
        out_num[a] += 1

    seen = [0] * (N+1)
    v0_list = []
    plus_sum = minus_sum = 0
    for v0 in range(1, N+1):
        if seen[v0]:
            continue
        v0_list.append(v0)
        seen[v0] = 1
        que = deque()
        que.append(v0)
        seq = []
        while que:
            v = que.popleft()
            seq.append(v)
            for u in adj[v]:
                if seen[u] == 0:
                    seen[u] = 1
                    que.append(u)
        p = s = 0
        for v in seq:
            if in_num[v] == 0:
                p += 1
            if out_num[v] == 0:
                s += 1
        if p == 0:
            p = 1
        if s == 0:
            s = 1
        plus_sum += p
        minus_sum += s
    if len(v0_list) == 1:
        flg = 1
        for v in range(1, N+1):
            if in_num[v] * out_num[v] == 0:
                flg = 0
        if flg:
            print(0)
            exit()
    print(max(plus_sum, minus_sum))


if __name__ == '__main__':
    main()