if name == 'main': n = int(input()) student_marks = {}

total_score = 0
average_score = 0

for _ in range(n):
    name, *line = input().split()
    scores = list(map(float, line))
    student_marks[name] = scores

query_name = input()
for st_score in student_marks[query_name]:
    total_score += st_score
average_score = total_score / len(student_marks[query_name])
print(f"{average_score:.2f}")