A, B, C, D, E = map(int, input().strip().split())

Ame_num = A*(B-C)
X=D

Ame_cost=0

for i in range(Ame_num):

    if i%10 != 0:
        Ame_cost = Ame_cost + X

    elif Ame_num%10 == 0 & E <= X:
        Ame_cost = Ame_cost + (X-E)
    
    elif Ame_num%10 == 0 & E > X:
        Ame_cost = Ame_cost + X

    else:
        Ame_cost = Ame_cost + D

print(Ame_cost)