A, B, C, D, E = map(int, input().split())
COUNT = (B - C) * A
ANSWER = 0
X = 0
for i in range(COUNT):
    if i == 0:
        ANSWER += D
        X = D
    else:
        if (i + 1) % 10 == 0:
            if E <= X:
                ANSWER += X - E
                X = X - E
            else:
                ANSWER += X
        else:
            ANSWER+=X
print(ANSWER)