program to calculate the area of triangle using heron's formula in python.
Three sides of the triangle is a, b and c:
a = float(input('Enter first side: '))
b = float(input('Enter second side: '))
c = float(input('Enter third side: '))
# calculate the semi-perimeter.
s = (a + b + c) / 2.
# calculate the area.
area = (s*(s-a)*(s-b)*(s-c)) ** 0.5.