total_stud = int(input())
list_stud = []
for i in range(total_stud):
    list_stud.append(list(input().split(' ')))
newList = dict([[i[0],list(map(float,i[1:]))] for i in list_stud])
query_marks = newList[input()]

average = sum(query_marks) / len(query_marks)

print(f'{average:.2f}')