// I'm not sure if this should pass, but _drf version probably should
fun main() {
    System.setIn(System.`in`.buffered())
    val (n, m) = readInts()
    val g = List(n) { mutableListOf<Int>() }
    val rg = List(n) { mutableListOf<Int>() }
    repeat(m) {
        val (a, b) = readInts()
        g[a - 1].add(b - 1)
        rg[b - 1].add(a - 1)
    }
    val topSort = mutableListOf<Int>()
    val used = BooleanArray(n) { false }
    for (i in 0 until n) {
        if (!used[i]) {
            fun dfs(v: Int) {
                used[v] = true
                for (v in g[v]) {
                    if (!used[v]) {
                        dfs(v)
                    }
                }
                topSort.add(v)
            }
            dfs(i)
        }
    }
    val color = IntArray(n) { -1 }
    var cc = 0
    for (i in topSort.reversed()) {
        if (color[i] == -1) {
            fun dfs(v: Int) {
                color[v] = cc
                for (v in rg[v]) {
                    if (color[v] == -1) {
                        dfs(v)
                    }
                }
            }
            dfs(i)
            cc++
        }
    }
    val cs = BooleanArray(cc) { true }
    for (v in g.indices) {
        for (to in g[v]) {
            if (color[to] != color[v]) {
                cs[color[to]] = false
            }
        }
    }
    println(cs.count { it })
}

private fun readStrings() = readln().split(" ")
private fun readInts() = readStrings().map { it.toInt() }