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 Python (3.4.3) (judge verdict: Runtime Error)

import sys

input = sys.stdin.readline


def f(l, c, s, n):
    if not l:
        if s == n:
            return -1
        return s

    if l[0] != c:
        return f(l[1:], c, s + 1, n)
    return f(l[1:], c + 1, s, n)

def main():
    n = int(input()[:-1])
    l = list(map(int, input()[:-1].split(" ")))

    c = 1
    s = 0
    tmp = 0
    while not l:
        if l[tmp] != c :
            s += 1
        else:
            c += 1
        tmp += 1

    res = s
    if s == n:
        res = -1

    print(f(l, 1, 0, n))

main()