def a(n):
    if n % 2 == 0:
        return n
    else:
        return (-1) * n

def b(n):
    suma = 0
    for i in range(1, n + 1):
        if i % 2 == 0:
            suma += (1 / i)
        else:
            suma -= (1 / i)
    return suma


def c(n, x):
    suma = 0
    t = 1
    for i in range(1, n + 1):
        t *= x
        suma += i * t
    return suma


def NWD(n, m):  # vol. 2 z wykladu 4
    if n < m:
        k = m
        m = n
        n = k
    while m > 0:
        k = n % m
        n = m
        m = k
    return n


def NWW(n, m):
    return n * m // NWD(n, m)


def ulamek(a, b):
    t = NWD(a, b)
    a = a // t
    b = b // t
    print(a, "/", b)


print(a(1331))
print(b(3))
print(c(10, 5))
print(NWW(10, 5))
ulamek(5, 100)