from math import *


def input_list():
    return list(map(int, input().split()))


def xzsort(alist):
    blist = []
    for j in range(len(alist)):
        minn = 0
        for i in range(len(alist)):
            if (alist[minn] > alist[i]):
                minn = i
        blist.append(alist[minn])
        alist[minn] = 114514
    return blist


def binarySearch(arr, l, r, x):
    if (r - l == 1):
        if (arr[l] == x):
            return l
        elif (arr[r] == x):
            return r
        else:
            return -1
    mid = floor((l + r) / 2)
    if (arr[mid] >= x):
        return binarySearch(arr, l, mid, x)
    else:
        return binarySearch(arr, mid, r, x)


a = input_list()
x = int(input())
print(binarySearch(xzsort(a), 0, len(a) - 1, x))