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 Java7 (OpenJDK 1.7.0) (judge verdict: Wrong Answer)

import java.util.*;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        // 整数の入力
        int N = sc.nextInt();
        int[] ary = new int[N];
        for (int i = 0; i < ary.length; i++) {
            ary[i] = sc.nextInt();
        }
        int broken = 0;
        boolean ok = true;
        while (broken != N) {
            //正解チェック
            int j = 0;
            ok = true;
            for (int i = 0; i < ary.length; i++) {
                if (ary[i] != 0)
                    j++;
                else
                    continue;

                if (ary[i] != j)
                    ok = false;
            }
            if (ok == true)
                break;
            //自分の位置以上の値が書かれていたら砕く
            j = 0;
            for (int i = 0; i < ary.length; i++) {
                if (ary[i] != 0)
                    j++;
                else
                    continue;
                if (ary[i] >= j) {
                    ary[i] = 0;
                    broken++;
                }
            }
        }

        if( broken == N )
            System.out.println(-1);
        else
            System.out.println(broken);
	}
}