Familias de Troia

def dfs(no):
    vis[no] = True
    for vizinho in adj[no]:
        if not vis[vizinho]: dfs(vizinho)

n, m = map(int, raw_input().split())

adj = {i:[] for i in range(1, n+1)}
vis = [False]*(n+1)

for i in range(m):
    aux, kek = map(int, raw_input().split())
    adj[aux] += [kek]

resp = 0
for j in range(1,n+1):
    if not vis[j]:
        resp += 1
        dfs(j)

print resp