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,cmath,math
c=[]
for s in sys.stdin:
    x,y=map(float,s[:-1].split(","))
    c+=[complex(x,y)]
c0=c[0]
c1=c[1]
r1,a1=cmath.polar(c1-c0)
s=0
for e in c[2:]:
    r2,a2=cmath.polar(e-c0)
    s+=r1*r2*math.sin(abs(a1-a2))/2
    r1,a1=r2,a2
print s