#############################################################

import sys
sys.setrecursionlimit(10**7)

from heapq import heappop,heappush
from collections import deque,defaultdict,Counter
from bisect import bisect_left, bisect_right
from itertools import product,combinations,permutations
from math import sin,cos
#from math import isqrt #DO NOT USE PyPy

ipt = sys.stdin.readline
iin = lambda :int(ipt())
lmin = lambda :list(map(int,ipt().split()))

#############################################################

W,Z,B = input().split()
W = int(W)
Z = int(Z)

if B == "0.5":
    print(W//2+Z//2+W+Z)
if B == "0.8":
    print(W*8//10+Z*8//10+W+Z)
if B == "1.2":
    print(W*12//10+Z*12//10+W+Z)
if B == "1.6":
    print(W*16//10+Z*16//10+W+Z)
if B == "2.0":
    print(W*2+Z*2+W+Z)