"""练习 10 进阶版：使用 bisect_left 查找有序列表中目标的第一个位置。"""
from bisect import bisect_left

n = int(input())
values = list(map(int, input().split()))[:n]
target = int(input())

position = bisect_left(values, target)
print(position if position < n and values[position] == target else -1)