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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;

namespace D___Brick_Break
{
    class Program
    {
        static void Main (string[] args)
        {
            var n = int.Parse (Console.ReadLine ());
            var input = Console.ReadLine ().Split (' ');
            var a = new List<int> ();
            for (var i = 0; i < n; i++)
            {
                a.Add (int.Parse (input[i]));
            }
            var b = 0;
            var c = 0;
            for (var i = 1; i <= n; i++)
            {
                for (var j = 0 + c; j < a.Count; j++)
                {
                    if (a[j] == i)
                    {
                        b++;
                        c = j + 1;
                        break;
                    }
                }
                if (b != i)
                {
                    if ((n - b) == n)
                    {
                        Console.WriteLine (-1);
                        break;
                    }
                    else
                    {
                        Console.WriteLine (n - b);
                        break;
                    }
                }
            }
        }
    }
}