vegetable_market

vegetable_price_1kg = float(input())
fruits_price_1kg = float(input())
all_vegetable_kg = int(input())
all_fruits_kg = int(input())

all_vegetable_kg = all_vegetable_kg * vegetable_price_1kg
all_fruits_kg = all_fruits_kg * fruits_price_1kg

income_all = all_vegetable_kg + all_fruits_kg

print(f'{income_all / 1.94:.2f}')