package main

import (
	"fmt"
)

func main() {
	var N, M int
	fmt.Scan(&N, &M)
	p := make([]int, 1+N)
	for i := 0; i < M; i++ {
		var A, B int
		fmt.Scan(&A, &B)
		p[B]++
	}

	m := 0
	for b := 1; b <= N; b++ {
		if p[b] == 0 {
			m++
		}
	}

	fmt.Println(m)
}