package main

import . "fmt"
import . "os"
import bf "bufio"

func main() {
	rd := bf.NewReader(Stdin)
	var n int
	Fscan(rd,&n)
	t := make(map[int][]int)
	for i := 1; i <= n; i++ {
		var a int
		Fscan(rd,&a)
		t[a] = append(t[a], i)
		if len(t[a]) > 2 {
			Println(0)
			Println()
			return
		}
	}
	lb, ub := 1, n
	for _, x := range t {
		if len(x) != 2 {
			continue
		}
		lb = max(lb, x[0])
		ub = min(ub, x[1])
	}
	ans := []any{}
	for i := lb; i < ub; i++ {
		ans = append(ans, i)
	}
	Println(len(ans))
	Println(ans...)
}