from decimal import Decimal, ROUND_HALF_UP

if __name__ == '__main__':
    n = int(input())
    student_marks = {}
    for _ in range(n):
        name, *line = input().split()
        scores = list(map(float, line))
        student_marks[name] = scores
    query_name = input()
    
    x = Decimal(str(sum(student_marks[query_name])/3))
    print(x.quantize(Decimal("0.01"), rounding = ROUND_HALF_UP))