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

if hito == 0:
    print(0)
    exit()

k = [D]
for i in range(2, ame+1):
    if i%10:
        k.append(k[-1])
    elif E <= k[-1]:
        k.append(k[-1]-E)
    else:
        k.append(k[-1])

print(sum(k))