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.

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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 PYTHON):

Solution:
import sys


def delta_s(p1,p2,p3):
    a = ( (p2[0]-p1[0])**2 + (p2[1]-p1[1])**2 )**0.5
    b = ( (p3[0]-p2[0])**2 + (p3[1]-p2[1])**2 )**0.5
    c = ( (p1[0]-p3[0])**2 + (p1[1]-p3[1])**2 )**0.5
    z = ( a+b+c )/2
    return (z*(z-a)*(z-b)*(z-c))**0.5
d = []

for s in sys.stdin:
    ds = map(float,s.split(","))
    d.append(ds)

d0 = d[0]
s = 0
for i in xrange(2,len(d)):
    s += delta_s(d[i],d[i-1],d0)
print s