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 Java (OpenJDK 11.0.6) (judge verdict: Wrong Answer)

import java.util.*;
class Main{
  public static int N;
  public static int[] A;
  public static int[] Check;
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    N = sc.nextInt();
    A = new int[N];
    for(int i=0;i<N;i++){
      A[i]=sc.nextInt();
    }
    Check = new int[N+1];
    int subR=N+1;
    for(int i = 0;i<N;i++){
      Check[i]=-1;
    }
    for(int i = 0;i<N;i++){
        if(A[i]==1){
          Check[1]=i;
          break;
        }
      }
    for(int checking=2;checking<=N;checking++){
      for(int i = Check[checking-1]+1;i<N;i++){
        if(A[i]==checking){
          Check[checking]=i;
          break;
        }
      }
      if(Check[checking]==0){
        break;
      }
    }
    for(int i = 0;i<=N;i++){
      if(Check[i]!=-1){
        subR=i;
      }
    }
    System.out.println(N-subR);
  }
}