#include <stdio.h>

int search(int arr[], int value, int l, int r) {
    int mid = (l + r) / 2;
    if (l > r) {
        return -1;
    }
    if (arr[mid] == value) {
        return mid;
    } else if (arr[mid] < value) {
        return search(arr, value, mid + 1, r);
    } else {
        return search(arr, value, l, mid - 1);
    }
}

int main() {
    int arr[1005], n, i, value;
    scanf("%d", &n);
    for (i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }
    scanf("%d", &value);
    printf("%d\n", search(arr, value, 0, n - 1));
    return 0;
}