DEBUG=False
def binary_search(A, T):
    L = 0
    R = len(A) - 1
    m=-1
    while L < R:  
        m = (L + R) // 2
        if A[m] < T:
            L = m + 1 
        elif A[m]>=T:
            R=m
    if A[L]==T:
        return L
    else:
        return -1
        

input_string = input().strip()
list_part, target_part = input_string.split(" ")
L = []
for s in list_part[1:-1].split(','):
    L.append(int(s))
t = int(target_part.strip())  

result = binary_search(L, t)
print(result)