N,M = map(int,input().split())
G = [[] for _ in range(N)]
rG = [[] for _ in range(N)]
for _ in range(M):
    u,v = map(int,input().split())
    u -= 1
    v -= 1
    G[u].append(v)
    rG[v].append(u)

def scc(N,G,rG):
    order = []
    used = [0] * N
    group = [None] * N
    def dfs(s):
        used[s] = 1
        for v in G[s]:
            if not used[v]:
                dfs(v)
        order.append(s)
    def rdfs(s,col):
        group[s] = col
        used[s] = 1
        for v in rG[s]:
            if not used[v]:
                rdfs(v,col)
    for i in range(N):
        if not used[i]:
            dfs(i)
    used = [0] * N
    label = 0
    for s in reversed(order):
        if not used[s]:
            rdfs(s,label)
            label += 1
    return label,group

def construct(N,G,label,group):
    G0 = [set() for _ in range(label)]
    GP = [[] for _ in range(label)]
    for v in range(N):
        lbs = group[v]
        for w in G[v]:
            lbt = group[v]
            if lbs == lbt:
                continue
            G0[lbs].add(lbt)
        GP[lbs].append(v)
    return G0,GP
        
label,group = scc(N,G,rG)
G0,GP = construct(N,G,label,group)
ans = label - 1
for i in GP:
    ans += len(i)
print(ans)