listString, targetString = input().split()
list_of_string_numbers = listString.lstrip('[').rstrip(']').split(',')
l = []
for s in list_of_string_numbers:
    l.append(int(s))

target = int(targetString)

x = -1
y = len(l)-1

while(x+1<y):
    m = (x+y)//2
    if(l[m]>=target):
        y = m
    else:
        x = m
if(l[y]==target):
    print(y)
else:
    print(-1)