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 JavaScript (node.js v5.12) (judge verdict: Accepted)

function Main(input) {
  var lines = input.split('\n');

  var num = Math.floor(lines[0]);
  
  var array = lines[1].split(' ').map(str => parseInt(str, 10));
  
  var currentNum = 1;
  var hummered = [];
  var flag = true;
  
  for (var i = 0; i < array.length; i++) {
    if (array[i] !== currentNum) {
      hummered.push(array[i]);
    } else if (array[i] === currentNum) {
      currentNum++;
    }
  }
  
  if (hummered.length === num) {
    var j = 1;
    for (var i = 0; i < num; i++) {
      if (array[i] !== j) {
        flag = false;
      }
    }
    if (flag) {
      console.log('1');
    } else {
      console.log('-1');
    }
  } else {
    console.log(hummered.length);
  }
  
}
Main(require('fs').readFileSync('/dev/stdin', 'utf8'));