with open("dfs.in", "r") as f:
    global n, m, graf
    n, m = [int(x) for x in f.readline().split()]
    graf = [list() for _ in range(n + 1)]
    for ls in f.readlines():
        ls = ls.split()
        graf[int(ls[0])].append(int(ls[1]))

viz = [0 for _ in range(n + 1)]


def df(s):
    viz[s] = 1
    for i in range(1, n + 1):
        if i in graf[s] and viz[i] == 0:
            df(i)


nrCompConexe = 0
for i in range(1, n + 1):
    if viz[i] == 0:
        nrCompConexe += 1
        df(i)


with open("dfs.out", "w") as f:
    f.write(str(nrCompConexe))