fishland

mackerel_price_1kg = float(input())
sprinkle_price_1kg = float(input())
bonito_count_kg = float(input())
safrid_count_kg = float(input())
mussles_count_kg = int(input())


bonito_price = (mackerel_price_1kg * 0.60) + mackerel_price_1kg
bonito_total_sum = bonito_count_kg * bonito_price
safrid_price_kg = (sprinkle_price_1kg * 0.8) + sprinkle_price_1kg
safrid_total_sum = safrid_count_kg * safrid_price_kg
mussles_price = 7.50
mussles_total_sum = mussles_count_kg * 7.50
total_sum = (bonito_total_sum + safrid_total_sum + mussles_total_sum)
print(f'{total_sum:.2f}')