import math

class Figura:
    def pole(self):
        pass

    def obwod(self):
        pass


class Trojkat(Figura):
    def __init__(self,x,y,z):
        self.x = x
        self.y = y
        self.z = z
        if self.x + self.y < self.z or self.x + self.z < self.y or self.y + self.z < self.x:
            raise Exception('To nie jest trojkat!')

    def pole(self):
        p = 1/2 * (self.x + self.y + self.z)
        return math.sqrt(p * (p - self.x) * (p - self.y) * (p - self.z))

    def obwod(self):
        return self.x + self.y + self.z


class Kwadrat(Figura):

    def __init__(self,a,b,c,d):
        self.a = a
        self.b = b
        self.c = c
        self.d = d
        if self.a != self.b or self.a != c or self.a != d:
            raise Exception('To nie jest kwadrat!')

    def pole(self):
        return self.a ** 2

    def obwod(self):
        return self.a * 4


class Prostokat(Figura):
    def __init__(self,a,b,c,d):
        self.a = a
        self.b = b
        self.c = c
        self.d = d
        if a == c and b == d:
            True
        elif a == b and c == d:
            self.b = c
            self.c = b
        elif a == d and b == c:
            self.c = d
            self.d = c
        else:
            raise Exception('To nie jest prostokat!')

    def pole(self):
        return self.a * self.b

    def obwod(self):
        return self.a * 2 + self.b * 2