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.

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.

Constraints

• All values in input are integers.
• $1 \leq N \leq 200000$
• $1 \leq a_i \leq N$

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.

见题面 Input 部分

见题面 Output 部分