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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int N = input.nextInt();
        int left;
        int start = -1;
        int result = 0;

        List<Integer> list = new ArrayList<>();

        for (int i = 0; i < N; i++) {
            list.add(input.nextInt());
        }
        left = 1;

        for (int i = 0; i < N; i++) {
            if (list.get(i) == 1){
                start = i;
                result = i;
                break;
            }
        }

        if (start == list.size() - 1){
            result = 0;
        }else if (start != -1){
            for (int i = start + 1; i < N; i++){
                if (left + 1 != list.get(i)){
                    result ++;
                }else {
                    left++;
                }
            }
        }else {
            result = -1;
        }

        System.out.println(result);
    }
}