func main()
	var n: int :: cui@inputInt()
	var m: int :: cui@inputInt()
	
	var a: []int :: #[n]int
	for(1, m)
		var u: int :: cui@inputInt() - 1
		var v: int :: cui@inputInt() - 1
		do a[v] :+ 1
	end for
	
	var ans: int :: 0
	for i(0, n - 1)
		if(a[i] = 0)
			do ans :+ 1
		end if
	end for
	do cui@print("\{ans}\n")
end func