from typing import List
class Solution:
#左闭右闭(注意边界条件)
def search(self, nums: List[int], target: int) -> int:
left,right=0,len(nums)-1
while left<=right:
mid=(left+right)//2
if nums[mid]<target:
left=mid+1
elif nums[mid]>target:
right=mid-1
else:
return mid
return -1
str=input()
nums=[int(i) for i in str.split()]
target=int(input())
a=Solution()
print(a.search(nums,target))