Problem: Write a program that reads the coordinates of the vertices of a convex n-sided polygon (a polygon whose internal angles are less than 180 degrees, that is, a polygon that is not dented) and outputs its area. The vertices are named Vertex 1, Vertex 2, Vertex 3, ... Vertex n according to the order of edge connections.

However, n is 3 or more and 20 or less. You can also use the following formula to find the area S from the lengths a, b, and c of the three sides of the triangle.

<image>



input

The input is given in the following format:


x1, y1
x2, y2
::
xn, yn


xi and yi are real numbers that represent the x and y coordinates of vertex i, respectively.

output

Outputs the area S (real number) on one line. The output can contain an error of 0.000001 or less.

Example

Input

0.0,0.0
0.0,1.0
1.0,1.0
2.0,0.0
1.0,-1.0


Output

2.500000

Solution (in PYTHON3):

Solution:
# AOJ 0079 Area of Polygon
# Python3 2018.6.17 bal4u

def calc_area(p):
	n, s = len(p), 0
	p.append(p[0])
	for i in range(n):
		s += (p[i].real-p[i+1].real)*(p[i].imag+p[i+1].imag)
	return abs(s)/2

p = []
while True:
	try: x, y = list(map(float, input().split(',')))
	except EOFError: break
	p.append(complex(x, y))
print(calc_area(p))