```go
package main

import (
	"bufio"
	"container/heap"
	"fmt"
	"os"
	"sort"
)

type Event struct {
	x   int
	h   int
	typ int
}

type IntHeap []int

func (h IntHeap) Len() int           { return len(h) }
func (h IntHeap) Less(i, j int) bool { return h[i] > h[j] }
func (h IntHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *IntHeap) Push(x interface{}) {
	*h = append(*h, x.(int))
}

func (h *IntHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[:n-1]
	return x
}

func main() {
	in := bufio.NewReader(os.Stdin)
	out := bufio.NewWriter(os.Stdout)
	defer out.Flush()

	var n int
	fmt.Fscan(in, &n)

	events := make([]Event, 0, 2*n)
	for i := 0; i < n; i++ {
		var h, l, r int
		fmt.Fscan(in, &h, &l, &r)
		events = append(events, Event{l, h, 1})
		events = append(events, Event{r, h, -1})
	}

	sort.Slice(events, func(i, j int) bool {
		return events[i].x < events[j].x
	})

	h := &IntHeap{}
	heap.Init(h)
	removed := make(map[int]int)

	getMax := func() int {
		for h.Len() > 0 {
			top := (*h)[0]
			if cnt, ok := removed[top]; ok && cnt > 0 {
				heap.Pop(h)
				removed[top]--
				if removed[top] == 0 {
					delete(removed, top)
				}
			} else {
				return top
			}
		}
		return 0
	}

	critical := make([][2]int, 0)
	currH := 0

	i := 0
	for i < len(events) {
		x := events[i].x
		for i < len(events) && events[i].x == x {
			if events[i].typ == 1 {
				heap.Push(h, events[i].h)
			} else {
				removed[events[i].h]++
			}
			i++
		}
		newH := getMax()
		if newH != currH {
			critical = append(critical, [2]int{x, newH})
			currH = newH
		}
	}

	fmt.Fprintln(out, 2*len(critical))
	if len(critical) > 0 {
		fmt.Fprintln(out, critical[0][0], 0)
		fmt.Fprintln(out, critical[0][0], critical[0][1])
		prevH := critical[0][1]
		for j := 1; j < len(critical); j++ {
			x, h := critical[j][0], critical[j][1]
			fmt.Fprintln(out, x, prevH)
			fmt.Fprintln(out, x, h)
			prevH = h
		}
	}
}
```