#include <stdio.h>
#include <stdint.h>
int binary_search(uint8_t *arr, uint8_t n, uint8_t key) {
// Your logic here
int l = 0;
int r = n-1;
while(l<=r){
int mid = l + (r-l)/2;
if(arr[mid]==key)
return mid;
if(arr[mid]<key)
l=mid+1;
else
r=mid-1;
}
return -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;
}