a, b, c, d, e = map(int, input().split())
n = a*(b-c)
if n == 0:
    print(0)
    exit()
ans = 0
x = -1
for i in range(1, n+1):
    if i == 1:
        ans += d
        x = d
        continue
    if i%10 != 0:
        ans += x
    else:
        if e <= x:
            ans += x-e
            x -= e
        else:
            ans += x
print(ans)