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:
import sys
from math import sqrt, hypot

def _hypot(p1, p2):
    return hypot(p2[0]-p1[0], p2[1]-p1[1])

def heron(p1, p2, p3):
    e1, e2, e3 = _hypot(p1, p2), _hypot(p2, p3), _hypot(p1, p3)
    z = (e1+e2+e3)/2
    return sqrt(z*(z-e1)*(z-e2)*(z-e3))

a = [tuple(map(float, l.split(","))) for l in sys.stdin]
result = 0
for p1, p2 in zip(a[1:], a[2:]):
    result += heron(a[0], p1, p2)
print(result)