type arr2d [][]int

func (a arr2d) Len() int           { return len(a) }
func (a arr2d) Less(i, j int) bool { return a[i][0] < a[j][0] }
func (a arr2d) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

func findMinArrowShots(points [][]int) (cnt int) {
	n := len(points)
	if n <= 1 {
		return n
	}
	sort.Sort(arr2d(points))
	beg, end := points[0][0], points[0][1]
	for i := 1; i < n; i++ {
		if b, e := points[i][0], points[i][1]; beg <= b && b <= end {
			beg = b
			if e < end {
				end = e
			}
		} else {
			cnt++
			beg, end = b, e
		}
	}
	cnt++
	return
}