def search(a,left,right):
    global x
    if left==right-1:
        return -1
    m=(left+right)//2
    if int(a[m])<x:
        return search(a,m,right)
    elif int(a[m])==x:
        return m+1
    else:
        return search(a,left,m)

a=[]
a=input().split()
x=int(input())
n=len(a)
left=-1
right=len(a)
print(search(a,left,right))