#include<stdio.h>
int binarysearch(int arr[],int n, int key ){
    int low=0,high=n-1;
    while (low<=high){
        int mid =(low+high )/2;
        if(arr[mid]==key)
        return mid;
        else if(arr[mid]<key)
        low=mid+1;
        else
        high=mid-1;
        
    }
    reurn -1;
    
}
int main(){
    int n;
    scanf("%d",&n);
    int arr[n];
    for (int i=0;i<n;i++)
    scanf("%d",&arr[i]);
    int key;
    scanf("%d",&arr[i]);
    int key ;
    scanf ("%d",&key);
    int result=binarysearch(arr,n,key);
    priuntf("%d",result);
    return 0;
}