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'''Given the weekly rental cost of a book X, the number of days you want to rent the book D, and your status as a staff member S (where S="true" if you are a staff member, otherwise S="false"), calculate the total rental cost based on the following rules:
 

1. The cost to rent the book for up to 7 days is X.
2. If D exceeds 7 days and you are not staff member, an additional charge of 2 Rs per extra day is applied.
3. If you are staff member, no extra charges apply for exceeding 7 days.
4. The full weekly cost X is charged even if you rent the book for less than 7 days.

Write a program to determine the total cost of renting the book.'''
'''Input
The input consists of three lines:
X: An integer representing the weekly rental cost of a book.
D: An integer representing the number of days the book was rented.
S: A string(either "true" or "false") indicating whether the person is a staff member'''


X = int(input())
D = int(input())
S = input()
if D<=7:
    print(X)
elif D>7:
    if S=="true":
        print(X)
    else:
        print(X+(2*(D-7)))