Problem:
Score : 400 points

Problem Statement

We have N bricks arranged in a row from left to right.

The i-th brick from the left (1 \leq i \leq N) has an integer a_i written on it.

Among them, you can break at most N-1 bricks of your choice.

Let us say there are K bricks remaining. Snuke will be satisfied if, for each integer i (1 \leq i \leq K), the i-th of those brick from the left has the integer i written on it.

Find the minimum number of bricks you need to break to satisfy Snuke's desire. If his desire is unsatisfiable, print -1 instead.

Constraints

All values in input are integers.

1 \leq N \leq 200000

1 \leq a_i \leq N

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 ... a_N

Output

Print the minimum number of bricks that need to be broken to satisfy Snuke's desire, or print -1 if his desire is unsatisfiable.

Sample Input 1

3
2 1 2

Sample Output 1

1

If we break the leftmost brick, the remaining bricks have integers 1 and 2 written on them from left to right, in which case Snuke will be satisfied.

Sample Input 2

3
2 2 2

Sample Output 2

-1

In this case, there is no way to break some of the bricks to satisfy Snuke's desire.

Sample Input 3

10
3 1 4 1 5 9 2 6 5 3

Sample Output 3

7

Sample Input 4

1
1

Sample Output 4

0

There may be no need to break the bricks at all.

Solution in Go (1.6) (judge verdict: Wrong Answer)

package main
import "fmt"

func deleteAryLeft(oAry []int, len int) []int{
	return oAry[len:]
}

func execMain4(num int, sAry []int) int {
	search_num := 1
	var ans_ary []int
	ans_ary = make([]int, num)
	bcnt := 0
	for ; ; {
		isHit := false
		for i := 0; i < len(sAry); i++ {
			if sAry[i] == search_num {
				tAry := sAry[0:i+1]
				sAry = deleteAryLeft(sAry, len(tAry))
				ans_ary = append(ans_ary, tAry[i])
				if len(tAry) > 1 {
					bcnt += len(tAry) - 1
				}
				search_num++
				isHit = true
				break
			}
		}

		if !isHit {
			bcnt += len(sAry)
			break
		}
	}

	if len(ans_ary) < 1 {
		return -1
	}

	return bcnt
}

func main() {
	var num int

	fmt.Scanf("%d", &num)
	sAry := make([]int, num)
	for i := 0; i < num; i++ {
		fmt.Scan(&sAry[i])
	}

	fmt.Print(execMain4(num, sAry))
}