#include <stdio.h>
#define MAX_SIZE 100

int readArray(int a[], int *n) {
    if (scanf("%d", n) != 1 || *n < 1 || *n > MAX_SIZE) return 0;
    for (int i = 0; i < *n; ++i)
        if (scanf("%d", &a[i]) != 1 || a[i] < -1000000 || a[i] > 1000000) return 0;
    return 1;
}

int binarySearch(const int a[], int n, int key) {
    int low = 0, high = n - 1;
    while (low <= high) {
        int mid = low + (high - low) / 2;
        if (a[mid] == key) return mid;
        if (key < a[mid]) high = mid - 1;
        else low = mid + 1;
    }
    return -1;
}

int main(void) {
    int a[MAX_SIZE], n, key;
    if (!readArray(a, &n) || scanf("%d", &key) != 1) {
        puts("Invalid input."); return 1;
    }
    for (int i = 1; i < n; ++i) {
        if (a[i] < a[i - 1]) { puts("Input must be sorted in ascending order."); return 1; }
    }
    int index = binarySearch(a, n, key);
    printf("Position: %d\n", index < 0 ? -1 : index + 1);
    return 0;
}