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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#pragma GCC optimize ("O3")
#include <bits/stdc++.h>
using namespace std;

#define pb push_back
#define mp make_pair
#define fs first
#define se second
#define pi 2*acos(0)
#define PI 3.14159265358979323846264338

typedef long long ll;
typedef unsigned long long ull;
typedef pair < int , int > pii;
typedef pair < ll , ll > pll;

const int N = 100010;
const int MX = 123456;
const int mod = (int)1e9 + 7;
const int base = 97;
const ull BS1 = 10000019ULL;
const int INF = (1 << 29);

template < class T > inline void fastScan(T &x){
    register char c = getchar();
    int neg = 0; x = 0;
    for(   ; (c < 48 || c > 57) && (c != '-'); c = getchar());
    if(c == '-') { neg = 1; c = getchar(); }
    for(   ; c > 47 && c < 58; c = getchar()){
        x = (x << 1) + (x << 3) + c - 48;
    }
    if(neg) x = -x;
}

char inp[N + N];

int main(){
  int n;
  fastScan(n);
  for(int i = 1; i <= n; i++){
    fastScan(inp[i]);
  }
  int d = 0, curr = 1;
  for(int i = 1; i <= n; i++){
    if(inp[i] == curr){
      curr++;
    } else {
      d++;
    }
  }
  if(d >= n){
    d = -1;
  }
  printf("%d\n", d);
  return 0;
}