Binary_Search

#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define ld long double
#define vi vector<int>
#define vll vector<long long>
#define pb push_back
#define p_b pop_back
using namespace std;

int Binary_Search(int arr[], int s, int e, int x){
    if(e >= s){
        int mid = s+(e-s)/2;
        if(arr[mid] == x){
            return mid;
        } else if(arr[mid] > x){
            return  Binary_Search(arr, s, mid-1, x);
        } else{
            return Binary_Search(arr, mid+1, e, x);
        }
    } else{
        return -1;
    }
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n; cin >> n;
    int arr[n];
    for(int i = 0; i < n; i++)  cin >> arr[i];
    int key; cin >> key;
    cout << Binary_Search(arr, 0, n-1, key) << "\n";
    return 0;
}