vis = [0 for i in range(100005)]
g = [[] for i in range(100005)]
with open('dfs.in', 'r') as fin:
    n, m = fin.readline().split()
    n = int(n)
    m = int(m)
    for line in fin:
        x, y = line.split()
        g[int(x)].append(int(y))

def dfs(x, vis):
    vis[x] = 1
    for y in g[x]:
        dfs(y, vis);

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

with open('dfs.out', 'w') as fout:
    fout.write(str(cc))