#include <stdio.h>
#include <stdint.h>
int binary_search(uint8_t *arr, uint8_t n, uint8_t key) {
// Your logic here
if(n==0) return -1;
int mid = n/2;
if(arr[mid] == key) return mid;
if(arr[mid] > key)
return binary_search(arr, mid, key);
else{
int res = binary_search(arr+mid+1, n-mid-1, key);
if(res == -1) return -1;
else
return res+mid+1;
}
}
int main() {
uint8_t n, key;
scanf("%hhu", &n);
uint8_t arr[100];
for (uint8_t i = 0; i < n; i++) {
scanf("%hhu", &arr[i]);
}
scanf("%hhu", &key);
int index = binary_search(arr, n, key);
printf("%d", index);
return 0;
}