A, B, C, D, E = map(int, input().split())
total = A * (B - C)

if total == 0:
    print(0)
else:
    total_cost = 0
    current_price = D
    total_cost += current_price

    for i in range(2, total + 1):
        if i % 10 == 0:
            if current_price >= E:
                current_price -= E
            # else, remains the same as before
        # Update the total cost with the current price
        total_cost += current_price

    print(total_cost)