package main

import (
	"fmt"
)

func main() {
	var n int
	if _, err := fmt.Scan(&n); err != nil {
		return
	}

	removed := make([]bool, 1001)
	for i := 0; i < n; i++ {
		var a, b int
		fmt.Scan(&a, &b)
		for j := a; j <= b; j++ {
			removed[j] = true
		}
	}

	var result []int
	for i := 1; i <= 1000; i++ {
		if !removed[i] {
			result = append(result, i)
		}
	}

	fmt.Print(len(result))
	for _, val := range result {
		fmt.Printf(" %d", val)
	}
	fmt.Println()
}