def parabol(a, b, n): # Метод парабол
    n = int(n)
    if n%2:
        n += 1
    h = (b-a)/n
    s = 0
    for i in range(n+1):
        if not i % n:
            k = 1
        elif i % 2:
            k = 4
        else:
            k = 2
        s += k*f(a + i*h)
    s *= h/3
    s = float(s)
    return s