peeeo

def f(x):
    a = -(1/6)*(x - 1)*(x - 2)*(x - 4)*(x + 2)
    return a

while True:
    values = input()
    valuesList = values.split(", ")
    valuesList = list(map(float, valuesList))
    summa = 0
    a = valuesList[0]
    b = valuesList[1]
    n = int(valuesList[2])
    if a > b:
        a, b = b, a
    x = a
    if (n == 0):
        break
    deltaX = (b - a) / n
    for i in range(0,n):
        integ = f(x + deltaX) + f(x)
        summa += (integ * deltaX / 2)
        x += deltaX
    print("{:.3f}".format(summa))