#include <stdio.h>
int binarysearch(int arr[], int n, int key) {
    int left = 0;
    int right = n - 1;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        if (arr[mid] == key)
            return mid;
        else if (arr[mid] < key)
            left = mid + 1;
        else
            right = mid - 1; 
    }
    return -1;
}
int main() {
    int n, key;
    scanf("%d", &n);
    int ages[n];
    for (int i = 0; i < n; i++) {
        scanf("%d", &ages[(i)];
    }
    scan("%d", key);
    int index = binarysearch(ages, n, key);
    printf("%d\n", index);
     return 0;
}