class Pravouhly_trojuhelnik(Tvar):
    def __init__(self, strana_a, strana_b, strana_c):
        self.strana_a = strana_a
        self.strana_b = strana_b
        self.strana_c = strana_c

    def __str__(self):
        return self.strana_c

    def obvod(self):
        return self.strana_a + self.strana_b + self.strana_c

    def obsah(self):
        return (self.strana_a * self.strana_b) / 2