# c03ex09.py
#    Area of triangle using Heron's formula

import math

def main():
    print "This program calculates the are of a triangle."
    print

    a, b, c = input("Enter the lengths of the sides (a,b,c): ")
    s = (a+b+c)/2.0
    area = math.sqrt(s*(s-a)*(s-b)*(s-c))

    print
    print "The area is", area, "square units."

main()