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: Accepted)

#import pysnooper
#import numpy
#import os,re,sys,operator
#from collections import Counter,deque
#from operator import itemgetter,mul
#from itertools import accumulate#,combinations,groupby,combinations_with_replacement,permutations
from sys import stdin,setrecursionlimit
#from bisect import bisect_left,bisect_right
#from copy import deepcopy
#import heapq
#import math
#import string
#from time import time
#from functools import lru_cache,reduce
#from math import factorial
#import sys
from fractions import gcd
setrecursionlimit(10**6)
input=stdin.readline

n=int(input())
a=[int(i) for i in input().split()]
ans=0
now=1
for i in range(n):
    if a[i]==now:
        now+=1
    else:
        ans+=1
print(-1 if ans==n else ans)