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