type array [][]int

func (a array) Len() int           { return len(a) }
func (a array) Less(i, j int) bool { return a[i][1] < a[j][1] }
func (a array) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

func findLongestChain(pairs [][]int) int {
	if len(pairs) == 0 {
		return 0
	}
	sort.Sort(array(pairs))
	pre, cnt := pairs[0][1], 1
	for _, p := range pairs {
		if pre < p[0] {
			pre = p[1]
			cnt++
		}
	}
	return cnt
}