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 PYTHON3):

Solution:
import sys,math

l=[list(map(float,i.split(","))) for i in sys.stdin]
S=0
for (i,j) in enumerate(l):
    xn,yn=j
    if i!=len(l)-1:
        xn_1,yn_1=l[i+1]
    else:
        xn_1,yn_1=l[0]
    a=math.sqrt(xn**2+yn**2)
    b=math.sqrt(xn_1**2+yn_1**2)
    c=math.sqrt((xn_1-xn)**2+(yn_1-yn)**2)
    z=(a+b+c)/2
    S+=math.sqrt(z*(z-a)*(z-b)*(z-c))
print(S)