n=int(input())
a=[]
for i in range(n):
    a.append(int(input()))
key=int(input())
i=0
j=len(a)-1
while i<=j:
    m=(i+j)//2
    if a[m]<key:
        i=m+1
    else:
        j=m-1
if i<n and a[i]==key:
    print(i+1)
else:
    print(-1)