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 Ruby (2.3.3) (judge verdict: Wrong Answer)

n = gets.to_i
nums = gets.split.map(&:to_i)
count = 0

flag = false
while !flag do
  before = nums.dup
  d_count = 0
  l = nums.length
  nums.delete_if.with_index do |num, i|
    #puts num
    #puts i
    if num > ((i + 1 - d_count) || num == nums[i-1-d_count]) && i != l-1
      d_count += 1
      count += 1
      true
    elsif i == l-1 && num > (i + 1 - d_count)
      d_count += 1
      count += 1
      true
    else
      false
    end
  end
  if nums == before
    flag = true
  end
  #print nums
end
#print nums

if nums.size == 0
  puts -1
else
  puts n - nums.uniq.length
end