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)

#include<bits/stdc++.h>
using namespace std;
#define IOS std::ios::sync_with_stdio(false),cin.tie(0),cout.tie(0)
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
template <class T>
struct rbtree: tree<T,null_type,less<T>, rb_tree_tag,tree_order_statistics_node_update>{};
#define IN freopen("in.txt", "r", stdin);
#define endl '\n'
#define mp make_pair
#define pb push_back
#define lowb lower_bound
#define eb emplace_back
#define fi first
#define se second
#define all(x) x.begin(),x.end()
#define sz(x) (int)x.size()
#define mem0(a) memset((a), 0, sizeof(a))
#define mem(a, b) memset((a), (b), sizeof(a))
typedef unsigned long long ull;
typedef long long ll;
typedef vector<int> VI;
typedef vector<ll> VL;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int inf = 0x3f3f3f3f;

const int N = 2e5+10;

int a[N];

int main(){
    IOS;
    int n; cin>>n;
    for(int i = 1; i <= n; i++)cin>>a[i];
    int cnt=1;
    for(int i = 1; i <= n; i++){
        if(a[i] == cnt){
            cnt++;
        }
    }
    cout<<n-cnt-1;


    return 0;
}