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 (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
)

func main() {
	n := readInt()
	a := make([]int, n)
	for i := 0; i < n; i++ {
		a[i] = readInt()
	}

	x := 1
	c := 0
	for i := 0; i < n; i++ {
		if a[i] == x {
			x++
		} else {
			c++
		}
	}

	if c == n {
		fmt.Println(0)
	} else {
		fmt.Println(c)
	}
}

var stdin *bufio.Scanner

func read() string {
	if stdin == nil {
		stdin = bufio.NewScanner(os.Stdin)
		stdin.Split(bufio.ScanWords)
		stdin.Buffer(make([]byte, bufio.MaxScanTokenSize), int(math.MaxInt32))
	}
	stdin.Scan()
	return stdin.Text()
}

func readInt() int {
	n, _ := strconv.Atoi(read())
	return n
}

func readFloat64() float64 {
	n, _ := strconv.ParseFloat(read(), 64)
	return n
}