tip = input()
if (tip == 'треугольник'):
    a = int(input())
    b = int(input())
    c = int(input())
    p = (a+b+c)/2
    St = ((p*(p-a)*(p-b)*(p-c))**0.5)
    print (St)

if (tip == 'прямоуголник'):
    a = int(input())
    b = int(input())
    Sp = a*b
    print (Sp)

if (tip == 'круг'):
    r = int(input())
    Sk = 3.14*(r**2)
    print (Sk)