海伦公式已知三边求面积

import math

a = float(input('a = '))
b = float(input('b = '))
c = float(input('c = '))
if a + b > c and a + c > b and b + c > a:
    print('周长: %f' % (a + b + c))
    s = (a + b + c) / 2
    area = math.sqrt(s * (s - a) * (s - b) * (s - c))
    print('面积: %f' % (area))
else:
    print('不能构成三角形')