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