import sys
sys.setrecursionlimit(5*10**5)
input = sys.stdin.readline
from collections import defaultdict, deque, Counter
from heapq import heappop, heappush
from bisect import bisect_left, bisect_right
from math import gcd

w,z,b = map(str,input().split())
w = int(w)
z = int(z)

d = {"0.5":15,
     "0.8":18,
     "1.2":22,
     "1.6":26,
     "2.0":30}

print((w+z)*d[b]//10)