p235

p235.py

def u(k, r):
    return (900 - 3*k)*pow(r, k-1)

def s(n, r):
    total = 0
    for k in range(1, n+1):
        total += u(k, r)
    return total

def compute():
    r = "1."
    goal = -600000000000
    while len(r) != 16:
        for x in range(0, 10):
            r1 = float(r + str(x))
            if s(5000, r1) < goal:
                r += str(x - 1)
                break
    return round(float(r), 12)