.

from decimal import Decimal

price_veg = float(input())
price_fruit = float(input())

kg_veg = int(input())
kg_fruits = int(input())

price_lv = price_fruit * kg_fruits + price_veg * kg_veg

price_eu = Decimal(price_lv / 1.94)
price_eu = round(price_eu, 2)

print(price_eu)